UC-NRLF 


SB    271    IhD 


REESE    LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Received 4 

Accessions  No.  *?_?./__<*0___       Shelf  No^... 

.L 


STELLAR    EVOLUTION 


BY  THE   SAME  AUTHOR. 


CLIMATE  AND  TIME  IN  THEIR  GEOLOGICAL 
RELATIONS  :  A  Theory  of  Secular  Changes 
of  the  Earth's  Climate.  By  JAMES  CROLL, 
of  H.  M.  Geological  Survey  of  Scotland. 
With  Maps  and  Illustrations.  12mo. 
Cloth,  $2.50. 

DISCUSSIONS  ON  CLIMATE  AND  COSMOLOGY. 
BY  JAMES  CROLL,  LL.D.,  F.R.S.  With 
Chart.  12mo.  Cloth,  $2.00. 


STELLAR  EVOLUTION 


AND  ITS  RELATIONS  TO 


GEOLOGICAL    TIME 


BY 


JAMES   CEOLL,  LL.D.,  F.R.S. 

AUTHOB  OP  'CLIMATE  AND  TIME,'  'CLIMATE  AND  COSMOLOGY,'  ETC. 


NEW    YORK 
D.   APPLETON    AND    COMPANY 

1889 


Authorized  Edition. 


PBEFACE. 


THERE  are  two,  and  only  two,  conceivable  sources  from 
which  the  prodigious  amount  of  energy  possessed  by 
our  sun  and  solar  system  can  possibly  have  been 
derived.  Not  only  are  these  two  sources  radically 
distinct  in  their  essential  nature,  but  both  are  admitted 
to  be  real  and  not  merely*  hypothetical  sources  of 
energy.  The  one  source  is  gravitation;  the  other, 
the  source  discussed  in  the  present  volume,  a  source 
to  which  attention  was  directed  some  twenty  years 
ago.  A  most  important  distinction  between  these  two 
sources  is  this :  the  amount  of  energy  available  from 
the  former  can  be  accurately  determined,  but  such  is 
not  the  case  in  regard  to  the  latter.  We  can  tell  with 
tolerable  certainty  the  greatest  amount  of  energy 
which  gravitation  could  possibly  have  conferred  on 
the  sun  and  solar  system ;  but  we  have,  at  present, 
no  means  of  assigning  a  limit  to  the  possible  amount 
which  might  have  been  derived  from  the  other  source. 
It  may  have  been  equal  to  that  which  gravitation 


vi  STELLAR  EVOLUTION 

could  afford,  or  it  may  have  been  twofold,  fourfold,  or 
even  tenfold  that  amount. 

We  have  evidently  in  this  case  a  means  of  deter- 
mining which  of  the  two  sources  will  ultimately  have 
to  be  adopted  as  the  source  to  which  the  energy  of  our 
solar  system  must  be  referred.  For  if  it  can  be  proved 
from  the  admitted  facts  of  geology,  biology,  and  other 
sciences,  that  the  amount  of  energy  in  the  form  of 
heat  which  has  been  radiated  into  space  by  the  sun 
during  geological  time  is  far  greater  than  the  amount 
which  could  possibly  have  been  derived  from  gravita- 
tion, this  will  undoubtedly  show  that  gravitation  can- 
not account  for  the  energy  originally  possessed  by  our 
system. 

The  First  Part  of  the  volume  is  devoted  to  the 
consideration  of  what  I  believe  to  be  the  probable 
origin  of  meteorites,  comets,  and  nebulae,  and  of  the 
real  source  from  which  our  sun  derived  his  energy. 
The  facts  which  support  the  theory  here  advocated, 
together  with  the  light  which  that  theory  appears  to 
cast  upon  those  facts,  are  next  considered ;  and  it  will 
be  found,  I  think,  that  the  theory  has  been  very  much 
strengthened  by  the  recent  important  spectroscopic 
researches  of  Mr.  Lockyer  and  others  in  reference  to 
the  constitution  of  nebulae.  The  Second  Part  of  the 
work  deals  with  the  evidence  in  support  of  the  theory 
derived  from  the  testimony  of  geology  and  biology  as 
to  the  age  of  the  sun's  heat.  vThe  Third,  and  last, 


PREFACE  vii 

Part  has  been  devoted  to  questions  relating  to  the 
pre-nebular  condition  of  the  universe,  and  the  bearing 
which  these  have  on  theories  of  stellar  evolution. 
Several  subjects  introduced  in  this  part  are  only  very 
briefly  treated.  These  will,  however,  be  considered 
at  greater  length  in  a  future  volume,  "  Determinism, 
not  Force,  the  Foundation-stone  of  Evolution,"  a  work 
of  a  more  general  and  abstract  character,  which  was 

commenced  many  years  ago. 

« 

PEIITH  :  January  2,  1889. 


CONTENTS. 


PART   I. 

THE  IMPACT  THEORY  OF  STELLAR  EVOLUTION. 

PAGB 

CONSIDERATION  OF  THE  FACTS  WHICH  SUPPOKT  THE   THEORY,  AND 
OF  THE  LIGHT  WHICH  THE  THEORY  APPEARS  TO  CAST  UPON 

THE  FACTS 12 

I.  Probable  Origin  of  Meteorites 12 

II.  Motion  of  the  Stars ;  how  of  such  different  velocities,  and 

always  in  straight  lines 14 

III.  Motion  of  the  Stars  not  due  to  their  mutual  attractions    .     14 

IV.  Probable  Origin  of  Comets 17 

V.  Nebulae 18 

1.  Origin  of  Nebulae 18 

2.  How  Nebulae  occupy  so  much  space  .        .        .        .18 

3.  Why  Nebulas  are  of  such  various  shapes       .        .    .     19 

4.  Broken  fragments  in  a  Gaseous  mass  of  an  exces- 

sively   high  temperature    the    First   stage  of    a 
Nebula 19 

5.  The  Gaseous  condition  the  Second  stage  of  a  Nebula    24 

6.  The   Gaseous   condition  Essential  to  the  Nebular 

Hypothesis 25 

7.  The  mass  must  have  possessed  an  excessive  tern- 

perature 26 

8.  Gravitation  could,  under  no  possible  condition,  have 

generated  the  Amount  of  Heat  required  by  the 
Nebular  Hypothesis 27 

9.  Condensation  the  Third  and  last  stage  of  a  Nebula  .     30 
10.  How  Nebulae  emit  such  feeble  Light     .        .        .     .    30 


x  STELLAE  EVOLUTION 

PAGE 

VI.  Binary  Systems 32 

VII.  Sudden  Outbursts  of  Stars 33 

VIII.  Star  Clusters    ' 34 

IX.  Age  of  the  Sun's  Heat :  a  Crucial  Test         •        .        .    .  34 


PART  II. 

EVIDENCE  IN  SUPPORT  OF  THE  THEORY 
FROM  THE  AGE  OF  THE  SUN'S  HEAT. 

TESTIMONY  OF  GEOLOGY  AND  BIOLOGY  AS  TO  THE  AGE  OF  THE 

SUN'S  HEAT 37 

Testimony  of  Geology  :  Method  employed 39 

The  Average  Eate  of  Denudation  in  the  Past  probably  not  much 

greater  than  at  the  Present 44 

How  the  Method  has  been  applied 47 

Method  as  applied  by  Professor  Haughton      .        .        •        .    .  50 
Method  as  applied  by  Mr.  Alfred  E.  Wallace       .        .        .        .51 

Method  as  applied  directly 52 

Evidence  from  "  faults  " 53 

Time  required  to  effect  the  foregoing  amount  of  Denudation  .    .  62 

Age  of  the  Earth  as  determined  by  the  Date  of  the  Glacial  Epoch  64 

Testimony  of  Biology 65 


PART  III. 

EVIDENCE     IN    SUPPORT    OF    THE    THEORY 

FROM  THE   PRE-NEBULAR   CONDITION  OF 

THE   UNIVERSE. 

Professor  A.  Winchell  on  the  pre-nebular  condition  of  matter    .  71 

Mr.  Charles  Morris  on  the  pre-nebular  condition  of  matter    .     .  75 

Sir  William  E.  Grove  on  the  pre-nebular  condition  of  matter      .  78 
Evolution  of  the  Chemical  Elements,  and  its  Eelations  to  Stellar 

Evolution 80 

Sir  Benjamin  Brodie  on  the  pre-nebular  condition  of  matter      .  84 

Dr.  T.  Sterry  Hunt  on  the  pre-nebular  condition  of  matter    .     .  85 

Professor  Oliver  Lodge  on  the  pre-nebular  condition  of  matter  .  87 


CONTENTS  xi 

PAGE 

Mr.  William  Crookes  on  the  pre-nebular  condition  of  matter .  .  90 
Professor  F.  W.  Clarke  on  the  pre-nebular  condition  of  matter  .  98 
Dr.  G.  Johnstone  Stoney  on  the  pre-nebular  condition  of  matter  99 

THE  IMPACT   THEOKY  IN  RELATION  TO  THE  FOREGOING  THEORIES 
OF  THE  PRE-NEBULAR  CONDITION  OF  MATTER     .        .        .     .  102 

The  Theories  do  not  account  for  the  Motion  of  the  Stars  .  .105 
The  Theories  do  not  account  for  the  Amount  of  Heat  required  .  106 

Evolution  of  Matter 107 

Objection  considered 109 

Can  we  on  Scientific  grounds  trace  back  the  Evolution  of  the 
Universe  to  an  Absolute  First  condition  ?  .        .  110 


£SE  LIBft^ 

OF  rue        lr 

UNIVERSITY 

^UFORNjU 

STELLAE   EVOLUTION. 

PART  I. 

TEE  IMPACT  THEORY  OF   STELLAR  EVOLUTION. 

UPWARDS  of  twenty  years  ago  *  the  theory — or,  I 
should  rather  say,  the  hypothesis — was  advanced2 
that  our  sun  was  formed  from  a  hot  gaseous  nebula 
produced  by  the  colliding  of  two  dark  stellar  masses ; 
and  that,  as  the  stars  are  suns  like  our  own,  they  in 
all  likelihood  had  a  similar  origin.  The  probability 
of  this  theory  has  been  very  much  strengthened  by 
the  facts,  both  astronomical  and  physical,  which  have 
accumulated  since  the  theory  was  enunciated.  Before 
proceeding  to  the  consideration  of  these  facts,  and  the 
conclusions  to  which  they  lead,  it  will  be  necessary  to 
give  a  statement  of  the  fundamental  principles  of  the 
theory. 

In   the   theory  here  discussed   the  truth  of   the 
nebular  hypothesis,  which   begins  by  assuming  the 

1  Philosophical  Magazine,    May    1868  ;     Climate    and    Time, 
chap.  xxi. ;  Quarterly  Journal  of  Science,  July  1877  ;  Phil.  Mag. 
July  1878  ;  Climate  and  Cosmology,  chaps,  xvii.  xviii.  and  xix. 

2  I  prefer  to  use  the  term  "  theory,"  with  the  above  understood 
qualification,  viz.  a  theory  in  its  hypothetical  stage. 


2  STELLAR  EVOLUTION 

existence  of  a  solar  nebulous  mass,  is  taken  for 
granted.  The  present  theory  deals  not  so  much  with 
the  nebulous  mass  itself  as  with  the  formation  of  the 
nebula,  and  with  those  causes  which  led  to  its  for- 
mation. For  convenience  of  reference,  and  to  prevent 
confusion,  I  have  called  it  the  "  Impact  Theory,"  by 
which  name  it  may  be  distinguished,  on  the  one  hand, 
from  the  nebular  theory,  and,  on  the  other  hand,  from 
the  meteoric  theory,  and  all  other  theories  which 
regard  gravitation  as  the  primary  source  of  the  solar 
energy. 

The  theory  starts  with  the  assumption  that  the 
greater  part  of  the  energy  possessed  by  the  universe 
exists  or  is  stored  up  in  the  form  of  the  motion 
of  stellar  masses.  The  amount  of  energy  which 
may  thus  be  stored  up  is  startling  to  contemplate. 
Thus  a  mass  equal  to  that  of  the  sun,  moving  with  a 
velocity  of  476  miles  per  second,  would  possess,  in 
virtue  of  that  motion,  energy  sufficient,  if  converted 
into  heat,  to  maintain  the  present  rate  of  the  sun's 
radiation  for  50,000,000  years.1  There  is  nothing 
extravagant  in  the  assumption  of  such  a  velocity.  A 
comet,  for  example,  having  an  orbit  extending  to  the 
path  of  the  planet  Neptune,  approaching  so  near  the 
sun  as  to  almost  graze  his  surface  in  passing,  would 
have  a  velocity  within  86  miles  of  what  we  have 
assumed.  Twice  this  assumed  velocity  would  give 
200,000,000  years'  heat;  four  times  the  velocity 
would  give  800,000,000  years'  heat ;  and  so  on. 

We  are  at  perfect  liberty  to  begin  by  assuming  the 

1  Pouillet's  estimate  of  the  rate  of  solar  radiation  is  here  taken. 


IMPACT  THEORY  OF  STELLAR  EVOLUTION     3 

existence  of  stellar  masses  in  motion ;  for  we  are  not 
called  upon  to  explain  how  the  masses  obtained  their 
motion,  any  more  than  we  have  to  explain  how  they 
came  to  have  their  existence.  If  the  masses  were 
created,  they  may  as  likely  have  been  created  in 
motion  as  at  rest ;  and  if  they  were  eternal,  they  may 
as  likely  have  been  eternally  in  motion  as  eternally  at 
rest. 

Eternal  motion  is  just  as  warrantable  an  assump- 
tion as  eternal  matter.  When  we  reflect  that  space 
is  infinite — at  least  in  thought — and  that,  for  aught 
we  know  to  the  contrary,  bodies  may  be  found  moving 
throughout  its  every  region,  we  see  that  the  amount 
of  energy  may  be  perfectly  illimitable. 

But,  illimitable  as  the  amount  of  the  energy  may 
be,  it  could  be  of  no  direct  service  while  it  existed 
simply  as  the  motion  of  stellar  masses.  The  motion, 
to  be  available,  must  be  transformed  into  heat :  the 
motion  of  translation  into  molecular,  or  some  other 
form  of  motion.  This  can  be  done  in  no  other 
way  than  by  arresting  the  motion  of  the  masses. 
But  how  is  such  motion  to  be  arrested  ?  How  are 
bodies  as  large  as  our  earth,  moving  at  the  rate  of 
hundreds  of  miles  per  second,  to  have  their  motion 
stopped  ?  According  to  the  theory  this  is  effected  by 
collision :  by  employing  the  motion  of  the  one  body  to 
arrest  that  of  the  other. 

Take  the  case  of  the  formation  of  our  sun  accord- 
ing to  the  theory.  Suppose  two  bodies,  each  one-half 
of  the  mass  of  the  sun,  moving  directly  towards  each 
other  with  a  velocity  of  476  miles  per  second.  These 


4  STELLAE  EVOLUTION 

bodies  would,  in  virtue  of  that  velocity,  possess 
4149  x  1038  foot-pounds  of  energy,  which  is  equal 
to  100,000,000,000  foot-pounds  per  pound  of  the 
mass ;  and  this,  converted  into  heat  by  the  stoppage 
of  their  motions,  would  suffice  to  maintain,  as  was 
previously  stated,  the  present  rate  of  the  sun's  radia- 
tion for  a  period  of  50,000,000  years.  It  must  be 
borne  in  mind  that,  while  476  miles  per  second  is  the 
velocity  at  the  moment  of  collision,  more  than  one- 
half  of  this  would  be  derived  from  the  mutual  attrac- 
tion of  the  two  bodies  in  their  approach  to  each 
other. 

Coming  in  collision  with  such  a  velocity,  the  result 
would  inevitably  be  that  the  two  bodies  would  shatter 
each  other  to  pieces.  But,  although  their  onward 
motions  would  thus  be  stopped,  it  is  absolutely  im- 
possible that  the  whole  of  the  energy  of  their  motions 
could  be  at  once  converted  into  heat ;  and  it  is  equally 
impossible  that  it  could  be  annihilated.  Physical 
considerations  enable  us  to  trace,  though  in  a  rough 
and  general  way,  the  results  which  would  necessarily 
follow.  The  broken  fragments,  now  forming  one 
confused  mass,  would  rebound  against  one  another, 
breaking  up  into  smaller  fragments,  and  flying  off  in 
all  directions.  As  these  fragments  receded  from  the 
centre  of  dispersion  they  would  strike  against_each 
other,  and,  by  their  mutual  impact,  become  shivered 
into  still  smaller  fragments,  which  would  in  turn  be 
broken  up  into  fragments  yet  smaller,  and  so  on  as  they 
proceeded  outwards.  This  is,  however,  only  one  part 
of  the  process,  and  a  part  which  would  certainly 


Of    THE 


UNIVEKSITY 


IMPACT   THEORY  OF  STELLAR  EVOLUTION     5 

take  place,  though  no  heat  were  generated  by  the 
collisions. 

A  far  more  effective  means  of  dispersing  the  frag- 
ments and  shattering  them  to  pieces  would  be  the 
expansive  force  of  the  enormous  amount  of  incandes- 
cent gas  almost  instantaneously  generated  by  the  heat 
of  collision.  The  general  breaking  up  of  the  two 
masses  and  the  stoppage  of  their  motions  would  be 
the  work  of  only  a  few  minutes,  or  a  few  hours  at 
most.  The  heat  evolved  by  the  arrested  motion  would, 
in  the  first  instance,  be  mainly  concentrated  on  the 
surface  layers  of  the  broken  blocks.  The  layers  would 
be  at  once  transformed  into  the  gaseous  condition, 
thus  enveloping  the  blocks  and  filling  the  interspaces. 
It  is  difficult  to  determine  what  the  temperature  and 
expansive  force  of  this  gas  would  at  the  moment  be, 
but  evidently  it  would  be  excessive  ;  for,  were  the  whole 
of  the  heat  of  the  arrested  motion  distributed  over 
the  mass,  it  would,  as  has  been  stated,  amount  to 
100,000,000,000  foot-pounds  per  pound  of  the  mass— 
an  amount  sufficient  to  raise  264,000  tons  of  iron  1°  C. 
Thus,  if  we  assume  the  specific  heat  of  the  gas  to  be 
equal  to  that  of  air  (viz.  *2374),  it  would  have  a 
temperature  of  about  300,000,000°  C.  or  more  than 
140,000  times  that  of  the  voltaic  arc. 

I  hardly  think  it  will  be  deemed  extravagant  to 
assume  that  at  the  moment  after  impact  the  tem- 
perature of  the  evolved  gas  would  be  at  least  as  great 
as  here  stated.  If  we  assume  it  to  be  so,  it  is  obvious 
that  the  broken  mass  would,  by  the  expansive  force 
of  the  generated  gas,  be  dispersed  in  all  directions, 


6  STELLAR  EVOLUTION 

breaking  up  into  fragments  smaller  and  smaller  as 
they  knocked  against  one  another  in  their  progress 
outwards  from  the  centre  of  dispersion;  and  these 
fragments  would,  at  the  same  time,  become  gradually 
converted  into  the  gaseous  state,  and  gradually  come 
to  occupy  a  space  as  large  as  that  embraced  in  our 
solar  system.  In  the  course  of  time  the  whole  would 
assume  the  gaseous  condition,  and  we  should  then 
have  a  perfect  nebula — intensely  hot,  but  not  very 
luminous.  As  its  temperature  diminished,  the  nebu- 
lous mass  would  begin  to  condense,  and  ultimately, 
according  to  the  well-known  nebular  hypothesis,  pass 
through  all  the  different  phases  of  rings,  planets,  and 
satellites  into  our  solar  system  as  it  now  exists. 

I  am  glad  to  find  that  the  theory,  in  one  of  its 
main  features,  has  been  adopted  by  Sir  William 
Thomson,1  the  highest  authority  we  have  on  all  points 
relating  to  the  source  of  the  sun's  heat. 

"We  cannot,"  says  Sir  William,  "help  asking  the 
question,  What  was  the  condition  of  the  sun's  matter 
before  it  came  together  and  became  hot  ?  (1)  It  may 
have  been  two  cool,  solid  masses,  which  collided  with 
the  velocity  due  to  their  mutual  gravitation  ;  or  (2), 
but  with  enormously  less  of  probability,  it  may  have 
been  two  masses  colliding  with  velocities  considerably 
greater  than  the  velocities  due  to  their  mutual  gravi- 
tation." 

1  Lecture  on  "  The  Probable  Origin,  the  Total  Amount,  and  the 
Possible  Duration  of  the  Sun's  Heat,"  delivered  at  theEoyal  Institu- 
tion on  January  21,  1887,  and  published  in  Nature  of  27th  of  the 
same  month.  The  lecture  was  afterwards  published  with  consider- 
able additions  and  alterations  in  the  Proceedings  of  the  Institution 
vol.  xii.  It  is  from  this  that  my  quotations  ate  taken. 


IMPACT   THEORY  OF  STELLAR  EVOLUTION     7 

He  adopts  the  first  of  these  suppositions.  "To 
fix  the  idea,"  he  continues,  "  think  of  two  cool,  solid 
globes,  each  of  the  same  mean  density  as  the  earth, 
and  of  half  the  sun's  diameter,  given  at  rest,  or  nearly 
at  rest,  at  a  distance  asunder  equal  to  twice  the  earth's 
distance  from  the  sun.  They  will  fall  together  and 
collide  in  exactly  half  a  year.  The  collision  will  last 
for  about  half  an  hour,  in  the  course  of  which  they 
will  be  transformed  into  a  violently  agitated  incan- 
descent fluid  mass  flying  outward  from  the  line  of  the 
motion  before  the  collision,  and  swelling  to  a  bulk 
several  times  greater  than  the  sum  of  the  original 
bulks  of  the  two  globes.  How  far  the  fluid  mass  will 
fly  out  all  around  from  the  line  of  collision  it  is  im- 
possible to  say.  The  motion  is  too  complicated  to  be 
fully  investigated  by  any  known  mathematical  method ; 
but  with  sufficient  patience  a  mathematician  might  be 
able  to  calculate  it  with  some  fair  approximation  to 
the  truth.  The  distance  reached  by  the  extreme  cir- 
cular fringe  of  the  fluid  mass  would  probably  be  much 
less  than  the  distance  fallen  by  each  globe  before 
the  collision,  because  the  translational  motion  of  the 
molecules  constituting  the  heafc  into  which  the  whole 
energy  of  the  original  fall  of  the  globes  becomes  trans- 
formed in  the  first  collision  is  probably  about  three- 
fifths  of  the  whole  amount  of  that  energy.  The  time 
of  flying  out  would  probably  be  less  than  half  a  year, 
when  the  fluid  mass  must  begin  to  fall  in  again  towards 
the  axis.  In  something  less  than  a  year  after  the  first 
collision  the  fluid  will  again  be  in  a  state  of  maximum 
crowding  round  the  centre,  and  this  time  probably 


8  STELLAR  EVOLUTION 

even  more  violently  agitated  than  it  was  imme- 
diately after  the  first  collision ;  and  it  will  again  fly 
outward,  but  this  time  axially  towards  the  places 
whence  the  two  glohes  fell.  It  will  again  fall  in- 
wards, and  after  a  rapidly  subsiding  series  of  quicker 
and  quicker  oscillations  it  will  subside,  probably  in 
the  course  of  two  or  three  years,  into  a  globular  star 
of  about  the  same  dimensions,  heat,  and  brightness, 
as  our  present  sun,  but  differing  from  him  in  this, 
that  it  will  have  no  rotation." l 

This  is  precisely  what  I  have  been  contending 
for  during  the  past  twenty  years,  with  the  simple 
exception  that  I  assume,  according  to  his  second  sup- 
position, that  the  "  two  masses  collided  with  velocities 
considerably  greater  than  the  velocities  due  to  mutual 
gravitation."  Sir  William  admits,  of  course,  my  sup- 
position to  be  quite  a  possible  one,  but  rejects  it  on 
the  supposed  ground  of  its  improbability.  His  reasons 
for  this,  stated  in  his  own  words,  are  as  follows : 

"  This  last  supposition  implies  that,  calling  the 
two  bodies  A  and  B  for  brevity,  the  motion  of  the 
centre  of  inertia  of  B  relatively  to  A  must,  when  the 
distance  between  them  was  great,  have  been  directed 
with  great  exactness  to  pass  through  the  centre  of 
inertia  of  A ;  such  great  exactness  that  the  rotational 
momentum  or  moment  of  momentum  after  collision 
was  no  more  than  to  let  the  sun  have  his  present 
slow  rotation  when  shrunk  to  his  present  dimensions. 
This  exceedingly  exact  aiming  of  the  one  body  at  the 
other,  so  to  speak,  is,  on  the  dry  theory  of  probability, 

1  Proceedings  of  the  Eoyal  Institution,  vol.  xii.  p.  15. 


IMPACT   THEOBY  OF  STELLAR  EVOLUTION     9 

exceedingly  improbable.  On  the  other  hand,  there 
is  certainty  that  the  two  bodies  A  and  B  at  rest  in 
space  if  left  to  themselves,  undisturbed  by  other  bodies 
and  only  influenced  by  their  mutual  gravitation,  shall 
collide  with  direct  impact,  and  therefore  with  no 
motion  of  their  centre  of  inertia,  and  no  rotational 
momentum  of  the  compound  body  after  the  collision. 
Thus  we  see  that  the  dry  probability  of  collision 
between  two  neighbours  of  a  vast  number  of  mutually 
attracting  bodies  widely  scattered  through  space  is 
much  greater  if  the  bodies  be  all  given  at  rest  than 
if  they  be  given  moving  in  any  random  directions  and 
with  any  velocities  considerable  in  comparison  with 
the  velocities  which  they  would  acquire  in  falling  from 
rest  into  collision." 

Sir  William  here  argues  that  the  second  suppo- 
sition is  far  less  probable  than  the  first,  because, 
according  to  it,  the  motion  of  the  one  body  relatively 
to  the  other  must,  in  order  to  strike,  be  directed  with 
great  exactness.  The  result,  in  such  a  case,  is  that 
collision  will  rarely  occur ;  whereas,  according  to  the 
first  supposition,  the  two  bodies  starting  from  a  state 
of  rest  will,  by  their  mutual  gravitation,  inevitably 
collide.  According  to  the  second  hypothesis  they  will 
generally  miss  ;  according  to  the  first  they  will  always 
collide. 

I  have  been  led  to  a  conclusion  directly  opposed 
to  Sir  William's.  The  fact,  that,  according  to  the 
second  supposition,  collisions  can  but  rarely  occur  is 
one  reason,  amongst  others,  why  I  think  that  suppo- 
sition to  be  true;  and  the  fact  that,  according  to  the  first 


10  STELLAR  EVOLUTION 

supposition,  collisions  must  frequently  occur  is  also 
one  reason,  amongst  others,  why  I  think  it  very  im- 
probable that  it  can  represent  the  true  condition  of 
things. 

It  by  no  means  adds  anything  to  the  probability 
of  the  first  supposition  to  assert  that,  according  to  it, 
such  collisions  will  occur  readily  and  frequently.  On 
the  contrary,  it  would  show  that  the  supposition  was 
the  less  likely  to  be  true.  If  the  collisions  were  in- 
sufficient in  character,  the  fewer  of  them  that  occurred, 
the  better ;  for  the  result  of  such  collisions  would 
simply  be  a  waste  of  the  potential  energies  of  the  uni- 
verse. We  should  in  this  case  have  an  innumerable 
host  of  imperfect  suns  without  planets,  or  with  at 
most  only  one  or  two,  and  these  at  no  great  distance 
from  the  luminary.  There  would  thus  be  evolved 
a  universe  without  any  grand  planetary  systems. 
There  is  still  another  objection  to  the  supposition. 
The  same  gravitating  force  which  makes  the  dark 
bodies  liable  to  come  into  collision  with  each  other 
must,  of  course,  make  them  equally  liable  to  come 
into  collision  with  the  luminous  bodies,  and  with  our 
sun  amongst  the  rest.  Our  sun  would,  accordingly, 
be  at  the  mercy  of  any  of  those  masses  which  might 
happen  to  come  within  the  reach  of  its  attractive  in- 
fluence. It  would  pull  the  mass  towards  it,  and  a 
collision  would  be  inevitable,  unless  it  so  happened 
that  a  transverse  motion  of  the  sun  itself  might  enable 
it  to  escape  destruction.  Even  in  such  a  case  it  could 
not  by  any  means  manage  to  get  rid  of  the  entangling 
mass. 


IMPACT   THEORY  OF  STELLAR  EVOLUTION   11 

All  this  risk,  in  so  far  as  gravitation  is  concerned, 
would  have  been  completely  averted  if  an  original 
projected  velocity  of  some  thirty  or  forty  miles  per 
second  had  been  conferred  on  the  dark  mass ;  for, 
in  this  case,  the  attractive  force  of  the  sun  would  fail  to 
arrest  its  motion,  and  the  mass  would  pass  onward 
through  space,  never  to  return.  This  simple  concep- 
tion of  an  original  motion  removes  entirely  those 
objections  which,  we  have  seen,  besets  the  supposition 
we  have  been  considering.  With  such  a  motion,  not 
only  would  the  risk  to  our  solar  system  be  removed, 
but  the  collisions  between  the  dark  bodies  themselves 
would  be  a  matter  of  rare  occurrence ;  and  hence  the 
energy  of  the  universe  would  be  conserved.  And  when 
a  collision  did  happen  it  would  be  on  a  grand  scale, 
and  the  result  would  be  not  an  imperfect  sun  without 
planets,  but  an  incandescent  nebula,  out  of  which, 
by  condensation,  a  complete  solar  system  would  be 
evolved.  In  fact,  within  the  whole  range  of  cosmical 
physics,  I  know  of  nothing  more  impressive  in  its 
sublime  simplicity  than  this  plan,  by  which  the  stability 
and  perfection  of  the  universe  is  thus  secured:  How 
vast  the  ends— how  simple  the  means  ! 


12  STELLAR  EVOLUTION 

CONSIDERATION  OF  THE  FACTS  WHICH  SUPPORT  THE 
THEORY,  AND  OF  THE  LIGHT  WHICH  THE  THEORY 
APPEARS  TO  CAST  UPON  THE  FACTS. 

I.  Probable  Origin  of  Meteorites. 

Eecent  researches  establish  beyond  doubt  that 
stars,  nebulae,  comets  and  meteorites,  do  not  differ 
much  from  our  earth  in  their  chemical  constitution. 
Meteorites,  it  is  true,  differ  in  their  physical  charac- 
teristics from  ordinary  rock  such  as  is  found  on  the 
earth's  surface.  But  it  is  possible,  if  not  probable, 
that  the  earth's  interior  mass  "  may,"  as  Sir  Henry 
Eoscoe  remarks,  "  partake  of  the  physical  nature  of 
these  metallic  meteorites,  and  that  if  we  could  obtain 
a  portion  of  matter  from  a  great  depth  below  the 
earth's  surface  we  should  find  it  exactly  corresponding 
in  structure  as  well  as  in  chemical  composition  with  a 
metallic  meteorite,  and  the  existence  of  such  interior 
masses  of  metallic  iron  may  go  far  to  explain  the 
well-known  magnetic  condition  of  our  planet."1  I 
think  there  can  be  little  doubt  that,  were  our  earth 
broken  up  into  small  fragments,  and  these  scattered 
into  space,  it  would  probably  be  impossible  to  dis- 
tinguish them  from  ordinary  meteorites.  The  two 
would  be  so  like  in  character  that  one  can  hardly 
resist  the  conviction  that  meteorites  are  but  the  frag- 
ments of  sidereal  masses  which  have  been  shattered 
by  collision.  That  meteorites  are  broken  fragments  is 
the  opinion  expressed  by  Sir  William  Thomson,  who 

1  Manchester  Science  Lectures,  Fifth  Series,  p.  31. 


IMPACT  THEOET  OF  STELLAR  EVOLUTION   13 

Bays  "  that  he  cannot  but  agree  with  the  common 
opinion  which  regards  meteorites  as  fragments  broken 
from  larger  masses,  and  that  we  cannot  be  satisfied 
without  trying  to  imagine  what  were  the  antecedents 
of  those  masses."  The  theory  we  have  been  consider- 
ing appears  to  afford  an  explanation  of  their  ante- 
cedents. According  to  it,  they  are  broken  fragments 
of  two  dark  stellar  masses  which  were  shattered  to 
pieces  by  collision.  After  what  has  been  stated  con- 
cerning the  production  of  the  gaseous  nebulaa  out  of 
which  our  solar  system  was  formed,  it  must  be  re- 
garded as  highly  improbable,  if  not  impossible,  that  the 
whole  of  the  fragments  projected  outwards  with  such 
velocity  should  be  converted  into  the  gaseous  condi- 
tion. Multitudes  of  the  smaller  fragments,  especially 
those  towards  the  outer  circumference  of  the  nebulous 
mass,  meeting  with  little  or  no  obstruction  to  their 
onward  progress,  would  pass  outwards  into  space 
with  a  velocity  which  would  carry  them  beyond  the 
risk  of  falling  back  into  the  nebula.  They  would  then 
continue  their  progress  in  their  separated  forms  as 
meteorites.  If  this  be  their  origin,  then  meteorites 
are  the  offspring  of  sidereal  masses,  and  not  their 
parents,  as  Mr.  Lockyer  concludes. 

These  meteorites  must  be  of  vast  antiquity,  for  if 
they  are  fragments  of  the  dark  bodies  then  they  must 
be  not  only  older  than  our  solar  system,  but  older 
than  the  nebula  from  which  that  system  was  formed. 
Some  of  them,  however,  may  have  come  from  other 
systems.  They  are  fragments  which  may  yet  cast 
some  light  on  the  history  of  the  dark  bodies. 
3 


14  STELLAR  EVOLUTION 

Comets,  bodies  which  in  many  points  seem  allied 
to  meteorites,  probably  have,  as  we  shall  shortly  see, 
a  similar  origin. 

II.  Motion  of  the  Stars  ;  how  of  such  different  velocities, 

and  always  in  straight  lines. 

It  will  be  only  when  the  two  bodies,  coming  from 
contrary  directions,  collide  with  equal  momentum 
that  the  entire  motion  will  be  stopped.  But  in  the 
case  of  stellar  masses  moving,  as  it  were,  at  ran- 
dom in  every  direction  this  is  a  condition  which  will 
but  rarely  occur.  Accordingly,  in  most  cases  the  re- 
sulting stars  will  have  more  or  less  motion.  In  short, 
the  stars  should,  according  to  the  theory,  be  moving 
in  all  directions  and  with  all  varieties  of  velocity. 
Further,  it  follows  that  these  motions  ought  to  be  in 
perfectly  straight  lines,  and  not  in  definite  orbits  of 
any  kind.  So  far  as  observation  has  yet  determined, 
all  these  conditions  seem  to  be  fulfilled.  Sometimes 
it  will  happen  that  the  two  bodies  will  strike  each 
other  obliquely.  In  this  case  the  resulting  scar,  both 
as  to  the  direction  and  velocity  of  its  motion,  will,  to 
a  large  extent,  be  the  resultant  of  the  two  concurrent 
forces. 

III.  Motion  of  the  Stars  not  due  to  their  Mutual 
Attractions. 

According  to  the  theory  the  absolute  motion  of  the 
stars  is  due,  not  to  the  influence  of  gravity,  but  to 
motions  which  originally  belonged  to  the  two  com- 
ponent masses  out  of  which  the  star  arose ;  motion 


IMPACT   THEORY  OF  STELLAR  EVOLUTION   15 

regarding  the  origin  of  which  science  can  no  more  in- 
form us  than  it  can  regarding  the  origin  of  the  masses 
themselves.  There  is  strong  presumptive  evidence 
that  the  motion  of  the  stars  is  due  to  this  cause.  We 
know  that  there  are  stars  which  have  a  far  greater 
velocity  than  can  result  from  gravitation,  such,  for 
example,  as  the  star  1830  Groombridge,  which  has 
a  velocity  of  200  miles  per  second.  Suppose,  with 
Professor  Newcomb,  that  the  number  of  stars  belong- 
ing to  the  universe  amounts  to  100,000,000,  and  that 
these  have,  on  the  average,  five  times  the  mass  of  the 
sun,  and  are  spread  out  in  a  layer  across  which  light 
requires  30,000  years  to  pass.  Then  computation 
shows  that,  unless  the  attractive  power  of  the  whole 
were  sixty-four  times  greater  than  it  really  is,  it  could 
not  have  conferred  on  Groombridge  the  motion  which 
it  possesses,  or  arrest  it  in  its  onward  course.1  We 
are  therefore  forced,  as  Professor  Newcomb  remarks, 
to  one  of  two  alternatives,  viz. :  "  Either  the  bodies 
which  compose  our  universe  are  vastly  more  massive 
and  numerous  than  telescopic  examination  seems  to 
indicate,  or  1830  Groombridge  is  a  runaway  star, 
flying  on  a  boundless  course  through  infinite  space, 
with  such  momentum  that  the  attraction  of  all  the 
bodies  of  the  universe  can  never  stop  it." 

As  regards  the  theory  we  are  discussing,  it  is  the 
same  which  alternative  is  taken,  for  both  are  equally 
favourable.  If  the  former,  then,  according  to  the 
theory  that  stellar  heat  had  its  origin  in  collision,  it  is 
presumptive  evidence  that  space  is  occupied  by  dark 
1  Newcomb's  Astronomy,  p.  487,  English  edition,  1878. 


16  STELLAE  EVOLUTION 

bodies  far  more  numerous  and  massive  than  the 
luminous  ones  which  the  telescope  reveals.  If  the 
latter,  viz.  that  the  star  has  a  velocity  which  never 
could  have  been  produced  by  attraction,  "  then,"  as 
says  Professor  Newcomb,  "  it  must  have  been  flying 
forward  through  space  from  the  beginning,  and, 
having  come  from,  an  infinite  distance,  must  now  be 
passing  through  our  system  for  the  first  and  only  time." 
The  probability  is,  however,  that  the  star  derived  its 
motion  from  the  source  from  which  it  derived  its 
light  and  heat ;  namely,  from  the  collision  of  the  two 
masses  out  of  which  it  arose.  If  the  star  is  ever 
to  be  arrested  in  its  onward  course,  it  must  be  by 
collision ;  but  such  an  event  would  be  its  final  end. 

There  are  other  stars,  such  as  61  Cygni,  e  Indi, 
Lalande  21258,  Lalande  21185,  yu,  Cassiopeiae,  and 
Arcturus,  possessed  of  motions  which  could  not  have 
been  derived  from  gravity.  And  there  are  probably 
many  more  of  which,  owing  to  their  enormous  dis- 
tances, the  proper  motions  have  not  been  detected. 
a  Centauri,  the  nearest  star  in  the  heavens,  by  less 
than  one-half,  is  distant  twenty-one  millions  of  mil- 
lions of  miles ;  and  there  are,  doubtless,  many  visible 
stars  a  thousand  times  more  remote.  A  star  at  this 
distance,  though  moving  transversely  to  the  observer 
at  the  enormous  rate  of  100  miles  per  second,  would 
take  upwards  of  thirty  years  to  change  its  position  so 
much  as  one  second,  and  consequently  1,800  years  to 
change  its  position  one  minute.  In  fact,  we  should 
have  to  watch  the  star  for  a  generation  or  two  before 
we  could  be  certain  whether  it  was  moving  or  not. 


IMPACT  THEORY  OF  STELLAR  EVOLUTION   17 

IV.  Probable  Origin  of  Comets. 

Great  difficulty  has  been  experienced  in  accounting 
for  the  origin  of  comets  upon  the  nebular  hypothesis. 
They  approach  the  sun  from  all  directions,  and  their 
motions,  in  relation  to  the  planets,  are  as  often  retro- 
grade as  direct.  Not  only  are  their  orbits  excessively 
elliptical,  but  they  are  also  inclined  to  the  ecliptic 
at  all  angles  from  0°  to  90°.  It  is  evidently  im- 
possible to  account  satisfactorily  for  the  origin  of 
comets  if  we  assume  them  all  to  have  been  evolved 
out  of  the  solar  nebula,  although  this  has  been 
attempted  by  M.  Faye  and  others.  Comets  are 
evidently,  as  Laplace  and  Professor  A.  Winchell  both 
conclude,  strangers  to  our  system,  and  have  come 
from  distant  regions  of  space.  If  they  belonged  to 
the  solar  system  they  could  not,  says  Professor  Win- 
chell, have  parabolic  and  hyperbolic  paths.  "  Only  a 
small  portion  of  the  comets,"  he  remarks,  "  are  known 
to  move  in  elliptic  orbits."  *  This  assumption  that  they 
are  foreigners  will  account  for  all  the  peculiarities  of 
their  motions ;  but  how  are  we  to  account  for  their 
coming  into  our  system  ?  How  did  they  manage  to 
leave  that  system  in  which  they  had  their  origin? 
If  a  comet  have  come  from  one  of  the  fixed  stars 
trillions  of  miles  distant,  the  motion  by  which  it 
traversed  the  intervenient  space  could  not,  possibly, 
have  been  derived  from  gravity.  We  are  therefore 
obliged  to  assume  that  the  motion  was  a  projected 
motion.  Comets,  in  all  probability,  have  the  same 

1  World  Life.  p.  27. 


18  STELLAR  EVOLUTION 

origin  as  meteorites.  The  materials  composing  them, 
like  those  of  the  meteorites,  were  probably  projected 
from  nebulae  by  the  expulsive  force  of  the  heat  of  con- 
cussion which  produced  the  nebulae.  Some  of  them, 
especially  those  with  elliptic  orbits,  may  have  possibly 
been  projected  from  the  solar  nebula. 

V.  Nebula. 

It  is  a  curious  circumstance  that  the  theory  here 
advanced  seems  to  afford  a  rational  explanation  of 
almost  every  peculiarity  of  nebulae,  as  I  have,  on 
former  occasions,  endeavoured,  at  some  length,  to 
prove.1 

1.  Origin  of  nebula. — We  have  already  seen  that 
the  theory  affords  a  rational  account  of  the  origin  of 
nebulas. 

2.  How  nebula  occupy  so  much  space. — It  accounts 
for  the  enormous  space  occupied  by  nebulae.     It  may 
be  objected  that,  enormous  as  would  be  the  original 
temperature  of  the   solar  system   produced  by   the 
primeval   collision,   it  would   nevertheless   be   insuf- 
ficient to  expand  the  mass,  against  gravity,  to  such 
an  extent  that  it  would  occupy  the  entire  space  in- 
cluded within  the  orbit  of  Neptune.     But  it  will  be 
perceived,  from  what  has  already  been  stated  regard- 
ing the  dispersion  of  the  materials  before  they  had 
sufficient  time  to  assume  the  gaseous  condition,  that 
this  dispersion  was  the  main  cause  of  the  gaseous 
nebula  coming  to  occupy  so  much  space.     And,  to  go 

1  Philosophical  Magazine,  July  1878 ;  Climate  (Mid  Cosmology \ 
Chap,  xix. 


IMPACT   THEORY  OF  STELLAR  EVOLUTION   19 

farther  back,  it  was  the  suddenness  and  almost  in- 
stantaneity  with  which  the  mass  would  receive  the 
entire  store  of  energy,  before  it  had  time  to  assume 
even  the  molten,  not  to  say  the  gaseous,  condition, 
which  led  to  tremendous  explosions,  followed  by  a 
wide  dispersion  of  materials. 

3.  Why    nebulae    are    of   such    varied    shapes. — 
Although  the  dispersion  of  the  materials  would  be  in 
all  directions,  it  would,  according  to  the  law  of  pro- 
bability, very  rarely  take   place   uniformly  in  every 
direction.      There    would    generally    be    a    greater 
amount   of  dispersion   in   some   directions  than   in 
others,  and  the  materials  would  thus  be  carried  along 
various  lines  and  to  diverse  distances  ;  and,  although 
gravity  would   tend   to   bring  the  widely  'scattered 
materials    ultimately    together    into    one    or    more 
spherical  masses,  yet,  owing  to  the  exceedingly  rari- 
fied  condition  of  the  gaseous  mass,  the  nebulae  would 
change  form  but  slowly. 

4.  Broken  fragments  in  a  gaseous  mass  of  an  ex- 
cessively high  temperature  the  first  stage  of  a  nebula. — 
From  what  has  already  been  shown,  it  will  be  seen 
that  after  the  colliding  of  the  two  dark  bodies  the 
first  condition  of  the  resulting  nebula  would  be  an 
enormous   space  occupied  by  broken  fragments  of 
all  sizes  dashing  against  each  other  with  tremendous 
velocities,  like  the  molecules  in  a  perfect   gas.     All 
the  interspaces  between   those   fragments  would  be 
entirely  filled  with   a   gaseous  mass,  which,   at  its 
earliest  stages  at  least,  as  in  the  case  of  the  solar 
nebula,  would  have  a  temperature  probably  more  than 


20  STELLAE  EVOLUTION 

one  hundred  thousand  times  that  of  the  voltaic  arc. 
Whether  such  a  mass  would  be  visible  is  a  point 
which  can  hardly  be  determined,  as  we  can  have  no 
experience  on  earth  of  a  gas  at  such  a  temperature. 

That  there  are  some  of  the  nebulae  which  appear 
to  consist  of  solid  matter  interspersed  in  a  gaseous 
mass  is  shown  by  the  researches  of  Mr.  Lockyer l 
and  others.  In  fact,  the  theory  is  held  by  Professor 
Tait2  that  nebulas  consist  of  clouds  of  stones — or 
meteor-swarms,  as  Mr.  Lockyer  would  term  them — 
in  an  atmosphere  of  hydrogen,  each  stone  of  which, 
moving  about  and  coming  into  collision  with  some 
other,  is  thereby  generating  heat  which  renders  the 
circumambient  gas  incandescent.  In  reference  to 
this  theory  of  Professor  Tait,  Mr.  Lockyer  says  that 
the  phenomena  of  the  spectroscope  can  be  quite  well 
explained  "  on  the  assumption  of  a  cloud  of  stones, 
providing  always  that  you  could  at  the  same  time 
show  reasonable  cause  why  these  clouds  of  stones 
were  '  banging  about '  in  an  atmosphere  of  hydro- 
gen."3 The  theory,  however,  does  not  appear  to 
afford  any  rational  explanation  of  this  banging  about 
of  the  stones  to  and  fro  in  all  directions  ;  for,  accord- 
ing to  it,  the  only  force  available  is  gravitation,  and 
this  can  produce  merely  a  motion  of  the  materials 
towards  the  centre  of  the  mass.  Under  these  con- 
ditions very  little  impinging  of  the  stones  against 
each  other  would  take  place.  But,  according  to  the 

1  Proceedings  of  Royal  Society,  vol.  xliii.  p.  117. 

2  Good  Words  for  1875,  p.  861. 
9  Manchester  Science  Lectures. 


IMPACT  THEORY  OF  STELLAR  EVOLUTION   21 

theory  here  adopted,  we  have  an  agency  incalculably 
more  effective  than  gravity,  one  which  accounts  not 
merely  for  the  impact  of  the  stones,  but  for  their  very 
existence  as  such,  inasmuch  as  it  explains  both  what 
they  are  and  whence  they  came. 

Mr.  Lockyer  has  recently  fully  adopted  Professor 
Tait's  suggestion  as  to  the  nature  and  origin  of  nebulae, 
and  has  endeavoured  to  give  it  further  development. 
He  considers  the  nebulae  to  be  composed  of  sparse 
meteorites,  the  collisions  of  which  give  the  nebulae 
their  temperature  and  luminosity.  He  divides  the 
nebulae  into  three  groups,  "  according  as  the  formative 
action  seems  working  towards  a  centre ;  round  a 
centre  in  a  plane,  or  nearly  so ;  or  in  one  direction 
only."  As  a  result  we  have  globular,  spheroidal, 
and  cometic  nebulae. 

Globular  nelulce  he  accounts  for  in  the  following 
manner.  "  If  we,"  he  says,  "  for  the  sake  of  the 
greatest  simplicity  consider  a  swarm  of  meteorites 
at  rest,  and  then  assume  that  others  from  without 
approach  it  from  all  directions,  their  previous  paths 
being  deflected,  the  question  arises  whether  there  will 
not  be  at  some  distance  from  the  centre  of  the  swarm 
a  region  in  which  collisions  will  be  most  valid.  If  we 
can  answer  this  question  in  the  affirmative,  it  will  follow 
that  some  of  the  meteorites  arrested  here  will  begin  to 
move  in  almost  circular  orbits  round  the  common 
centre  of  gravity. 

"  The  major  axes  of  these  orbits  may  be  assumed  to 
be  not  very  diverse,  and  we  may  further  assume  that, 
to  begin  with,  one  set  will  preponderate  over  the  rest. 


22  STELLAE  EVOLUTION 

Their  elliptic  paths  may  throw  the  periastron  passage 
to  a  considerable  distance  from  the  common  centre  of 
gravity ;  and  if  we  assume  that  the  meteorites  with 
this  common  mean  distance  are  moving  in  all  planes, 
and  that  some  are  direct  and  some  retrograde,  there 
will  be  a  shell  in  which  more  collisions  will  take  place 
than  elsewhere.  Now,  this  collision  surface  will  be 
practically  the  only  thing  visible,  and  will  present  to 
us  the  exact  and  hitherto  unexplained  appearance  of 
a  planetary  nebula — a  body  of  the  same  intensity  of 
luminosity  at  its  edge  and  centre — thus  putting  on  an 
almost  phosphorescent  appearance. 

"If  the  collision  region  has  any  great  thickness, 
the  centre  should  appear  dimmer  than  the  portion 
nearer  the  edge. 

"  Such  a  collision  surface,  as  I  use  the  term,  is 
presented  to  us  during  a  meteoric  display  by  the  upper 
part  of  our  atmosphere."  * 

Spheroidal  nebula,  he  considers,  are  produced  by 
the  rotation  of  what  was  at  first  a  globular  rotating 
swarm  of  meteorites. 

Cometic  nebula  are  explained,  he  considers,  "  on 
the  supposition  that  we  have  either  a  very  condensed 
swarm  moving  at  a  very  high  velocity  through  a  sheet 
of  meteorites  at  rest,  or  the  swarm  at  rest  surrounded 
by  a  sheet,  all  moving  in  the  same  direction." 

In  an  able  and  interesting  work,  which  seems 
almost  utterly  unknown  in  England,2  Professor 

1  Proc.  of  Royal  Society,  vol.  xliv.  p.  5. 

2  World  Life,   or  Comparative  Geology,  by  Alexander  Winchell, 
LL.D.,  Professor  of  Geology  and  Palaeontology  in  the  University  of 
Michigan.     Chicago :  S.  C.  Griggs  &  Co.    1883. 


IMPACT   THEOEY  OF  STELLAR  EVOLUTION   23 

Winchell  has  advanced  views  similar  to  those  of 
Tait  and  Lockyer  regarding  the  nature  and  origin 
of  nebulae.  But  he,  in  addition,  discusses  the 
further  question  of  the  origin  of  those  swarms. 
I  shall  have  occasion  to  refer  to  Professor  Win- 
chell's  views  more  fully  when  we  come  to  the 
consideration  of  the  pre-nebular  condition  of  the 
universe. 

Amongst  the  first  to  advance  the  meteoric  hypo- 
thesis of  the  origin  and  formation  of  the  solar  system 
was  probably  the  late  Mr.  Kichard  A.  Proctor.  This 
was  done  in  his  work,  "  Other  Worlds  than  Ours/' 
published  in  1870.  "Under  the  continual  rain  of 
meteoric  matter,"  he  says,  "  it  may  be  said  that  the 
earth,  sun,  and  planets  are  growing.  Now,  the  idea 
obviously  suggests  itself  that  the  whole  growth  of  the 
solar  system,  from  its  primal  condition  to  its  present 
state,  may  have  been  due  to  processes  resembling 
those  which  we  now  see  taking  place  within  its  bounds." 
He  further  adds :  "  It  seems  to  me  that  not  only  has 
this  general  view  of  the  mode  in  which  our  system  has 
reached  its  present  state  a  greater  support  from  what 
is  now  actually  going  on  than  the  nebular  hypothesis 
of  Laplace,  but  that  it  serves  to  account  in  a  far  more 
satisfactory  manner  for  the  principal  peculiarities  of 
the  solar  system.  I  might,  indeed,  go  farther,  and 
say  that  where  those  peculiarities  seem  to  oppose 
themselves  to  Laplace's  theory  they  give  support  to 
those  I  have  put  forward."  l  He  then  goes  on  to  show 
the  points  wherein  his  theory  seems  to  him  to  offer  a 

1  Other  Worlds,  chap.  ix. 


24  STELLAR  EVOLUTION 

better  explanation  of  those  peculiarities  than  that  of 
Laplace. 

5.  The  gaseous  condition  the  second  stage  of  a 
nebula. — The  second  stage  obviously  follows  as  a 
necessary  consequence  from  the  first;  for  the  frag- 
ments, in  the  case  under  consideration,  possess  energy 
in  the  form  of  motion,  which,  with  the  heat  of  their 
circumambient  vapour,  is  more  than  sufficient  not  only 
to  convert  the  fragments  into  the  gaseous  state,  but  to 
produce  complete  dissociation  of  the  chemical  elements. 
The  complete  transformation  of  the  first  stage  into 
the  second  must,  therefore,  be  simply  a  matter  of 
time. 

According  to  the  laws  of  probability  it  may,  how- 
ever, sometimes  happen  that  the  two  original  dark 
bodies  will  not  collide  with  force  sufficient  to  confer 
on  the  broken  fragments  the  energy  required  to  con- 
vert them  all  into  the  gaseous  condition.  The  result 
in  this  case  would,  no  doubt,  be  that  the  untransformed 
fragments,  drawn  together  by  their  mutual  attractions, 
would  collide  and  form  an  imperfect  star  or  sun,  with- 
out a  planet.  Such  a  star  might  continue  luminous 
for  a  few  thousands  or  perhaps  a  few  millions  of 
years,  as  the  case  might  be,  when  it  would  begin  to 
fade,  and  finally  disappear.  We  have  here  an  im- 
perfect nebula,  resulting  in  an  imperfect  star.  In 
short,  we  should  have  in  those  stellar  masses,  on  a 
grand  scale,  what  we  witness  every  day  around  us 
in  organic  nature,  viz.  imperfect  formations.  Such 
occasional  imperfections  give  variety  and  add  per- 
fection to  the  whole.  How  dreary  and  monotonous 


IMPACT   THEORY  OF  STELLAR  EVOLUTION   25 

would  nature  be,  were  every  blade  of  grass,  every 
plant,  every  animal,  and  every  face  we  met  formed 
after  the  most  perfect  model ! 

6.  The  gaseous  condition  essential  to  the  nebular 
hypothesis. —  It  is  found  that  the  density  of  the 
interior  planets  of  our  solar  system  compared  with 
that  of  the  more  remote  is  about  as  five  to  one.  The 
obvious  conclusion  is  that  there  is  a  preponderance  of 
the  metallic  elements  in  the  interior  planets  and  of 
metalloids  in  the  exterior.  It  thus  becomes  evident, 
as  Mr.  Lockyer  has  so  clearly  shown,1  that  when  our 
solar  system  existed  in  a  nebulous  condition  the  metallic 
or  denser  elements  would  occupy  the  interior  portion 
of  the  nebula  and  the  metalloids  the  exterior.  Taking 
a  section  of  this  nebula  from  its  centre  to  its  circum- 
ference, the  elements  would  in  the  main  be  found 
arranged  according  to  their  densities  :  the  densest  at 
the  centre,  and  the  least  dense  at  the  circumference. 
If  we  compare  the  planets  with  their  satellites,  we 
find  the  same  law  holding  true.  The  satellites  of 
Jupiter,  for  example,  have  a  density  of  about  only 
one-fifth  of  that  of  the  planet,  or  about  one  twenty- 
fifth  of  that  of  our  earth,  showing  that  when  the 
planet  was  rotating  as  a  nebulous  mass  the  more 
dense  elements  were  in  the  central  parts  and  the  less 
dense  at  the  outer  rim,  where  the  satellites  were  being 
formed.  Again,  if  we  take  the  case  of  our  globe,  we 
find,  as  Mr.  Lockyer  remarks,  the  same  distribution 
of  materials,  proving  that  when  the  earth  was  in  the 
nebulous  state  the  metallic  elements  chiefly  occupied 

1  Manchester  Science  Lectures 


26  STELLAR  EVOLUTION 

the  central  regions,  and  the  metalloids  those  outer 
parts  which  now  constitute  the  earth's  crust. 

All  these  facts  show  that  the  sifting  and  sorting 
of  the  chemical  elements  according  to  their  densities 
must  have  taken  place  when  our  solar  system  was  in 
the  condition  of  a  nebula.  But,  further,  it  seems  im- 
possible that  this  could  have  taken  place  had  the 
materials  composing  the  nebula  been  in  the  solid 
form,  even  supposing  that  they  had  taken  the  form  of 
clouds  of  stones. 

It  is  equally  impossible  that  the  nebula  could  have 
been  in  the  fluid  or  liquid  state  during  this  process. 
This  is  obvious,  for  the  nebula  must  then  have 
occupied,  at  least,  the  entire  space  within  the  orbit  of 
the  most  remote  planet.  But  our  solar  system  in  the 
liquid  condition  could  not  occupy  one-millionth  part 
of  that  space.  It  is  therefore  evident  that  the  nebula 
must  have  been  in  the  state  of  a  gas,  and  a  gas  of 
extreme  tenuity. 

7.  The  mass  must  have  possessed  an  excessive 
temperature. — There  is  ample  evidence,  Mr.  Lockyer 
thinks,  to  show  that  the  temperature  of  the  solar 
nebula  was  as  great  as  that  of  the  sun  at  the  present 
time.  But  I  think  it  is  extremely  probable  that,  in 
some  of  its  stages,  the  nebula  had  a  very  much  higher 
temperature  than  that  now  possessed  by  the  sun. 
There  must,  during  the  sifting  period,  have  been 
complete  chemical  dissociation,  so  as  to  keep  the 
metals  and  the  metalloids  uncombined,  and  thus 
allow  the  elements  to  arrange  themselves  according 
to  their  densities.  The  nebula  hypothesis,  remarks 


IMPACT  THEORY  OF  STELLAE  EVOLUTION    27 

Mr.  Lockyer,  "  is  almost  worthless  unless  we  assume 
very  high  temperatures,  because,  unless  you  have  heat 
enough  to  get  perfect  dissociation,  you  will  not  have  that 
sorting  out  which  always  seems  to  follow  the  same  law." 

8.  Gravitation  could,  under  no  possible  condition,  have 
generated  the  amount  of  heat  required  by  the  nebular 
hypothesis. — The  nebular  hypothesis  does  not  profess 
to  account  for  the  origin  of  nebulae.  It  starts  with 
matter  existing  in  space  in  the  nebulous  condition, 
and  explains  how,  by  condensation,  suns,  planets  &c. 
are  formed  out  of  it.  In  fact,  it  begins  at  the  middle 
of  a  process  :  it  begins  with  this  fine,  attenuated 
material  in  the  process  of  being  drawn  together  and 
condensed  under  the  influence  of  attraction,  and  pro- 
fesses to  explain  how,  as  the  process  goes  on,  a  solar 
system  necessarily  results.  To  simplify  our  inquiry 
we  shall  confine  our  attention  to  the  solar  nebula,  and 
consider  in  the  first  place  how  far  condensation  may 
be  regarded  as  a  sufficient  source  of  heat. 

A.  Condensation.  —  The  heat  which  our  nebula 
could  have  derived  from  condensation  up  to  the  time 
that  Neptune  was  detached  from  the  mass,  no  matter 
how  far  the  outer  circumference  of  the  mass  may  have 
originally  extended  beyond  the  orbit  of  that  planet, 
could  not  have  amounted  to  over  7^50  °f  a  ther- 
mal unit  (772  foot-pounds)  for  each  cubic  foot.  It  is 
perfectly  obvious  that  this  amount  could  not  have 
produced  the  dissociation  required ;  and  without  the 
required  dissociation  Neptune  could  never  have  been 
formed.  Further,  it  is  physically  impossible  that  the 
materials  of  which  our  solar  system  are  composed 


28  STELLAR  EVOLUTION 

could  have  existed  in  the  gaseous  state  in  a  cool  con- 
dition prior  to  condensation.  Unless  possessed  of 
great  heat,  even  hydrogen  could  not  exist  in  stellar 
space  in  the  gaseous  form  ;  and  far  less  could  carbon, 
iron,  platinum,  &c.  Before  Neptune  could  have  been 
formed  the  whole  of  the  materials  of  the  system  must 
have  possessed  heat,  not  only  sufficient  to  reduce  them 
to  the  gaseous  state,  but  sufficient  to  produce  com- 
plete dissociation.  But  by  no  conceivable  means  could 
gravitation  have  conferred  this  amount  of  heat  by  the 
time  that  the  mass  had  condensed  to  just  within  the 
limits  of  the  orbit  of  Neptune. 

B.  Solid  globes  colliding  under  the  influence  of 
gravity  alone. — As  we  have  already  seen,  the  view  has 
been  adopted  by  Sir  W.  Thomson  that  the  solar 
nebula  may  have  resulted  from  the  colliding  of  cold, 
solid  globes  with  the  velocity  due  to  their  mutual 
gravitation  alone.  He  states  his  views  as  follows  : 

"  Suppose,  now,  that  29,000,000  cold,  solid  globes, 
each  of  about  the  same  mass  as  the  moon,  and 
amounting  in  all  to  a  total  mass  equal  to  the  sun's, 
are  scattered  as  uniformly  as  possible  on  a  spherical 
surface  of  radius  equal  to  one  hundred  times  the 
radius  of  the  earth's  orbit,  and  that  they  are  left  ab- 
solutely at  rest  in  that  position.  They  will  all  com- 
mence falling  towards  the  centre  of  the  sphere,  and 
will  meet  there  in  250  years,  and  every  one  of  the 
29,000,000  globes  will  "then,  in  the  course  of  half  an 
hour,  be  melted,  and  raised  to  a  temperature  of  a  few 
hundred  thousand  or  a  million  degrees  Centigrade. 
The  fluid  mass  thus  formed  will,  by  this  prodigious 


IMPACT   THEORY  OF  STELLAR  EVOLUTION   29 

heat,  be  exploded  outwards  in  vapour  or  gas  all  round. 
Its  boundary  will  reach  to  a  distance  considerably  less 
than  one  hundred  times  the  radius  of  the  earth's 
orbit  on  first  flying  out  to  its  extreme  limit.  A 
diminishing  series  of  out -and -in  oscillations  will 
follow,  and  the  incandescent  globe,  thus  contracting 
and  expanding  alternately,  in  the  course,  it  may  be,  of 
300  or  400  years,  will  settle  to  a  radius  of  forty  times 
the  radius  of  the  earth's  orbit."  l 

The  reason  which  he  assigns  for  the  incandescent 
globe  settling  down  at  a  radius  forty  times  that  of  the 
earth's  orbit  is  as  follows :  "  The  radius  of  a  steady 
globular  gaseous  nebula  of  any  homogeneous  gas  is 
40  per  cent,  of  the  radius  of  the  spherical  surface 
from  which  its  ingredients  must  fall  to  their  actual 
positions  in  the  nebula  to  have  the  same  kinetic 
energy  as  the  nebula  has." 

If  the  solar  nebula  thus  produced  would  be  swelled 
out  into  a  spherical  incandescent  mass  with  a  radius 
40  times  the  radius  of  the  earth's  orbit,  simply  because 
the  globes  fell  from  a  distance  of  100  times  the  radius 
of  that  orbit,  then  for  a  similar  reason  the  mass  would 
have  a  radius  of  400  times  that  of  the  earth's  orbit 
had  the  globes  fallen  from  a  distance  of  1,000  times 
the  radius,  and  400,000  times  if  the  globes  had  fallen 
from  a  distance  of  1,000,000  times  the  radius,  and 
two-fifths  of  any  conceivable  distance  from  which 
they  may  have  fallen. 

Supposing  all  this  to  be  physically  possible,  which 
it  undoubtedly  is  not,  still  the  heat  generated  would  not 

1  Proceedings  of  Royal  Institution,  vol.  xii.  p.  16. 


80  STELLAR  EVOLUTION 

be  sufficient ;  for,  whatever  the  radius  of  the  nebula 
might  be,  its  entire  energy,  both  kinetic  and  potential, 
is  simply  what  is  obtained  from  gravitation,  and  this, 
as  we  have  seen,  is  insufficient. 

9.  Condensation  the  third  and   last  condition  of  a 
nebula. — According  to   the  gravitation   theory,   con- 
densation is  the  first  stage  of  a  nebula  as  well  as  the 
last ;  for,  according  to  it,  gravity  is  the  force  which 
both  collects  together  the  scattered  materials  and  gives 
them  their  heat.1     Before  condensation  begins  there 
can,  according  to  the  gravitation  theory,  be  no  such 
thing  as  a  nebula  properly  so  called.     The  materials 
exist,  of  course,  but  they  do  not  exist  in  the  form  of  a 
nebula.    According  to  the  impact  theory  which  I  here 
advocate,  condensation   cannot    begin   till   after  the 
nebula  has  begun  to  lose  the  heat  with  which  it  was 
originally  endowed. 

10.  Hoiv  nebula  emit  such  feeble  light. — The  light 
of  nebulae  is  mainly  derived  from  glowing  hydrogen 
and   nitrogen    in    a   condition    of    extreme    gaseous 
tenuity ;  and  it  is  well  known  that  these  gases  are 
exceedingly  bad  radiators.     The  oxyhydrogen  flame, 
although  its  temperature  is  surpassed  only  by  that  of 
the  voltaic  arc,  gives  a  light  so  feeble  as  to  be  scarcely 
visible  in  daylight.     The  small  luminosity  of  nebulae 
is,  however,  mainly  due  to  a  different  cause.     The 

1  Laplace  held  a  more  accurate  view  of  the  primitive  condition 
of  the  solar  nebula.  He  considered  that,  owing  to  intense  heat,  the 
solar  mass  became  expanded  to  the  limits  of  the  remotest  planetary 
orbit  of  our  system ;  that,  in  cooling,  it  began  slowly  to  condense  ; 
and  that,  as  condensation  went  on,  planet  after  planet  became  de- 
tached from  the  mass.  Laplace,  however,  offered  no  explanation 
of  the  manner  in  which  the  primitive  nebula  obtained  its  heat. 


IMPACT   THEORY  OF  STELLAR  EVOLUTION    31 

enormous  space  occupied  by  those  bodies  is  not  so 
much  due  to  the  heat  which  they  possess  as  to  the 
fact  that  their  materials  were  dispersed  into  space 
before  they  had  time  to  pass  into  the  gaseous  con- 
dition ;  so  that,  by  the  time  that  this  latter  state  was 
assumed,  the  space  occupied  was  far  greater  than  was 
demanded  either  by  the  temperature  or  by  the  amount 
of  heat  which  they  originally  received.  If  we  adopt 
the  nebular  hypothesis  of  the  origin  of  our  solar 
system,  we  must  assume  that  our  sun's  mass,  when 
in  the  condition  of  a  nebula,  extended  beyond  the 
orbit  of  the  planet  Neptune,  and  consequently  filled  the 
entire  space  included  within  that  orbit.  Even  supposing 
Neptune's  orbit  to  have  been  its  outer  limit,  which, 
obviously,  was  not  the  case,  it  would  nevertheless 
have  occupied  274,000,000,000  times  the  space  it 
does  at  present.  We  shall  assume,  as  before,  that 
50,000,000  years'  heat  was  generated  by  the  con- 
cussion. Of  course,  there  might  have  been  twice  or 
even  ten  times  that  quantity;  but  it  is  of  no  im- 
portance what  amount  is  in  the  meantime  adopted. 
Enormous  as  50,000,000  years'  heat  is,  it  yet  gives, 
as  we  shall  presently  see,  only  32  foot-pounds  of 
energy  for  each  cubic  foot.  The  amount  of  heat  due 
to  concussion  being  equal,  as  before  stated,  to 
100,000,000,000  foot-pounds  for  each  pound  of  the 
mass,  and  a  cubic  foot  of  the  sun  at  his  present 
density  of  1'43  weighing  89  pounds,  each  cubic  foot 
must  have  possessed  8,900,000,000,000  foot-pounds. 
But  when  the  mass  was  expanded  sufficiently  to 
occupy  274,000,000,000  times  its  original  space 


82  STELLAR  EVOLUTION 

(which  it  would  do  when  it  extended  to  the  orbit  of 
Neptune),  the  heat  possessed  by  each  cubic  foot 
would  then  amount  to  only  32  foot-pounds. 

In  point  of  fact  it  would  not  even  amount  to  so 
much,  for  a  quantity  equal  to  upwards  of  20,000,000 
years'  heat  would  necessarily  be  consumed  in  work 
against  gravity  in  the  expansion  of  the  mass,  all  of 
which  would,  of  course,  be  given  back  in  the  form  of 
heat  as  the  mass  contracted.  During  the  nebulous 
condition,  however,  this  quantity  would  exist  in  an 
entirely  different  form,  so  that  only  19  out  of  the 
32  foot-pounds  per  cubic  foot  generated  by  concussion 
would  then  exist  as  heat.  The  density  of  the  nebula 
would  be  only  162J8>100  that  of  hydrogen  at  ordinary 
temperature  and  pressure.  The  19  foot-pounds  of 
heat  in  each  cubic  foot  would  thus  be  sufficient  to 
maintain  an  excessive  temperature ;  for  there  would 
be  in  each  cubic  foot  only  ^^  of  a  grain  of  matter. 
But,  although  the  temperature  would  be  excessive,  the 
quantity  both  'of  light  and  heat  in  each  cubic  foot 
would  of  necessity  be  small.  The  heat  being  only  &  of 
a  thermal  unit,  the  light  emitted  would  certainly  be 
exceedingly  feeble,  resembling  very  much  the  electric 
light  in  a  vacuum-tube. 

VI.  Binary  Systems. 

The  theory  affords  a  rational  explanation  of  the 
origin  of  binary  stars.  Binary  stars,  in  so  far  as 
regards  their  motion,  follow  also,  of  course,  as  a  con- 
sequence, from  the  gravitation  theory.  If  two  bodies 
come  into  grazing  collision,  "  they  will,"  says  Sir 


IMPACT  THEOEY  OF  STELLAR  EVOLUTION   33 

William  Thomson,  "  commence  revolving  round  their 
common  centre  of  inertia  in  long  elliptic  orbits.  Tidal 
interaction  between  them  will  dimmish  the  eccentri- 
cities of  their  orbits,  and,  if  continued  long  enough, 
will  cause  them  to  revolve  in  circular  orbits  round 
their  centre  of  inertia."  l  This  conclusion  was  pointed 
out  many  years  ago  by  Dr.  Johnstone  Stoney. 

VII.  Sudden  Outbursts  of  Stars. 

The  case  of  a  star  suddenly  blazing  forth  and  then 
fading  away,  such  as  that  observed  by  Tycho  Brahe 
in  1572,  may  be  accounted  for  by  supposing  that  the 
star  had  been  struck  by  one  of  the  dark  bodies — an 
event  not  at  all  impossible,  or  even  improbable.  In 
some  cases  of  sudden  outbursts,  such  as  that  of  Nova 
Cygni,  for  example,  the  phenomenon  may  result  from 
the  star  encountering  a  swarm  of  meteorites.  The 
difficulty  in  the  case  of  Nova  Cygni  is  to  account  for 
the  very  sudden  decline  of  its  brilliancy.  This  might, 
however,  be  explained  by  supposing  thai  the  outburst 
of  luminosity  was  due  to  the  destruction  of  the 
meteorites,  and  not  to  any  great  increase  of  heat  pro- 
duced in  the  star  itself.  A  swarm  of  meteorites  con- 
verted into  incandescent  vapour  would  not  be  long  in 
losing  its  brilliancy. 

Mr.  Lockyer  thinks  that  the  outburst  was  produced 
by  the  collision  of  two  swarms  of  meteorites,  and  not 
by  the  collision  of  the  meteorites  with  a  previously 
existing  star.2 

1  Proceedings  of  Royal  Institution,  vol.  xii.  p.  15. 

2  Proceedings  of  the  Royal  Society,  vol.  xliii.  p.  140. 


84  STELLAR  EVOLUTION 

Amongst  the  millions  of  stars  occupying  stellar 
space  catastrophes  of  this  sort  may,  according  to  the 
theory,  be  expected  sometimes  to  happen,  although, 
like  the  collisions  which  originate  stars  themselves, 
they  must,  doubtless,  be  events  of  but  rare  occurrence. 

VIII.  Star  Clusters. 

A  star  cluster  will  result  from  an  immensely  wide- 
spread nebula  breaking  up  into  a  host  of  separate 
nuclei,  each  of  which  becomes  a  star.  The  irregular 
manner  in  which  the  materials  would,  in  many  cases, 
be  widely  distributed  through  space  after  collision 
would  prevent  a  nebula  from  condensing  into  a  single 
mass.  Subordinate  centres  of  attraction  would  be 
established,  as  was  long  ago  shown  by  Sir  William 
Herschel  in  his  famous  memoir  on  the  formation 
of  stars ; l  and  around  these  the  gaseous  particles 
would  arrange  themselves  and  gradually  condense 
into  separate  stars,  which  would  finally  assume  the 
condition  of  a  cluster. 

IX.  Age  of  the  Sun's  Heat:  a  Crucial  Test. 

When  we  come  to  the  question  of  the  age  of  the 
sun's  heat,  and  the  length  of  time  during  which  that 
orb  has  illuminated  our  globe,  it  becomes  a  matter  of 
the  utmost  importance  which  of  the  two  theories  is 
to  be  adopted.  On  the  age  of  the  sun's  heat  rests 
the  whole  question  of  geological  time.  A  mistake 
here  is  fundamental.  If  gravitation  be  the  only 
source  from  which  the  sun  derived  its  heat,  then  life 

1  Philosophical  Transactions  for  1811. 


IMPACT  THEORY  OF  STELLAR  EVOLUTION    35 


on  the  globe  cannot  possibly  date  farther  back  than 
20,000,000  years  ;  for  under  no  possible  form  could 
gravitation  have  afforded,  at  the  present  rate  of 
radiation,  sufficient  heat  for  a  longer  period.  It  will 
not  do  to  state  in  a  loose  and  general  way,  as  has 
been  frequently  done,  that  the  sun  may  have  been 
supplying  our  globe  with  heat  at  its  present  rate 
for  20,000,000  or  100,000,000  years,  for  gravita- 
tion could  have  done  no  such  thing  ;  a  period  of 
20,000,000,  not  100,000,000,  years  is  the  lowest  which 
is  admissible  on  that  theory.  Not  even  that  length  of 
time  would  be  actually  available  ;  for  this  period  is 
founded  on  Pouillet's  estimate  of  the  rate  of  solar 
radiation,  which  has  been  proved  by  Langley  to  be 
too  small,  the  correct  rate  being  1-7  times  greater. 
"  Thus,"  as  says  Sir  W.  Thomson,  "  instead  of  Helm- 
holtz's  20,000,000  years,  we  have  only  12,000,000." 
But  the  12,000,000  years  would  not  in  reality  be 
available  for  plant  and  animal  life  ;  for  undoubtedly 
millions  of  years  would  elapse  before  our  globe  could 
become  adapted  for  either  flora  or  fauna.  If  there  is 
no  other  source  of  heat  for  our  system  than  gravita- 
tion, it  is  doubtful  if  we  can  calculate  on  much  more 
than  half  that  period  for  the  age  of  life  on  the  earth. 
Professor  Tait  probably  over-estimates  the  time  when 
he  affirms  "that  10,000,000  years  is  about  the  ut- 
most that  can  be  allowed,  from  the  physical  point 
of  view,  for  all  the  changes  that  have  taken  place  on 
the  earth's  surface  since  vegetable  life  of  the  lowest 
known  form  was  capable  of  existing  there."  l  And  this 

1  Recent  Advances  in  Physical  Sciences,  p.  175. 


36  STELLAE  EVOLUTION 

is  certainly  about  all  that  can  ever  be  expected  from 
gravitation;  mathematical  computation  has  demon- 
strated that  it  can  give  no  more.  The  other  theory, 
founded  on  motion  in  space — a  cause  as  real  as 
gravitation — labours  under  no  such  limitation.  Ac- 
cording to  it,  so  far  at  least  as  regards  the  store  of 
energy  which  may  have  been  possessed  by  the  sun, 
plant  and  animal  life  may  date  back,  not  to  10,000,000 
years,  but  to  a  period  indefinitely  more  remote.  In 
fact,  there  is  as  yet  no  known  limit  to  the  amount  of 
heat  which  this  cause  may  have  produced ;  for  this 
depended  upon  the  velocities  of  the  two  bodies  at  the 
moment  prior  to  collision,  and  what  these  velocities 
were  we  have  no  means  of  knowing.  They  might 
have  been  500  miles  a  second,  or  5,000  miles  a  second, 
for  anything  which  can  be  shown  to  the  contrary. 
Of  course  I  by  no  means  affirm  that  it  is  as  much 
as  100,000,000  years  since  life  began  on  our  earth ; 
but  I  certainly  do  affirm  that,  in  so  far  as  a  possible 
source  of  the  sun's  energy  is  concerned,  life  may  have 
begun  at  a  period  as  remote. 


PAET  II. 

EVIDENCE  IN  SUPPORT  OF  THE  THEORY  FROM 
THE  AGE  OF  THE  SUN'S  HEAT. 

TESTIMONY   OF   GEOLOGY   AND   BIOLOGY   AS    TO    THE 
AGE    OF    THE    SUN?S    HEAT. 

THE  question  which  we  have  now  to  consider  is — to 
which  of  the  two  theories  does  geology  lend  its  testi- 
mony ?  Will  the  length  of  time  which,  according  to 
the  gravitation  theory,  can  possibly  be  allotted  satisfy 
the  requirements  of  geology  ?  In  short,  are  the  facts 
of  geology  reconcilable  with  the  theory  ?  If  not,  the 
theory  must  be  abandoned. 

Before  the  period  when  geologists  felt  that  they 
were  limited  to  time  by  physical  considerations,  the 
most  extravagant  opinions  prevailed  in  regard  to  the 
length  of  geological  epochs.  So  long  as  the  physicist 
continued  to  state  in  a  loose  and  general  way  that  the 
sun  might  have  been  supplying  our  earth  with  heat 
at  his  present  rate  for  the  past  100,000,000  years, 
no  very  serious  difficulty  was  felt ;  but  when  geologists 
came  to  understand  that  ten  or  twenty  millions  of 
years  were  all  that  could  be  granted  to  them,  the  con- 
dition of  matters  was  entirely  altered.  The  belief 
that  the  mathematical  physicist  must  be  right  in  his 


38  STELLAB  EVOLUTION 

views  as  to  the  age  of  the  sun's  heat,  and  that  there 
is  no  possibility  of  a  longer  period  heing  admitted, 
seems  at  present  to  be  leading  geologists  towards  the 
opposite  extreme  in  regard  to  the  length  of  geological 
time.  Attempts  have  been  recently  made  to  compress 
the  geological  history  of  our  globe  into  the  narrow 
space  allotted  by  the  physicist.  The  attempt  is  hope- 
less, as  well  as  injurious  to  geological  science.  What 
misleads  is  not  the  belief  that  gravitation  could  not 
possibly  afford  a  supply  of  heat  sufficient  for  more 
than  20,000,000  years,  for  this  is  true;  it  is  the 
belief  that  there  was  no  other  source  of  heat  than 
gravity. 

We  shall  now  consider  the  evidence  which  geology 
seems  to  afford  as  to  the  age  of  the  sun's  heat. 
Geology  is  quite  competent  to  render  aid  on  this 
point,  for  the  sun's  heat  must  be  at  least  as  old  as 
life  on  this  globe  ;  and  the  record  of  the  rocks  tells  us 
when  this  life  first  appeared.  We  require,  however, 
to  be  able  to  measure  the  time  which  has  elapsed  since 
these  records  were  left.  What  we  want  is  absolute 
time ;  not  relative  time.  Much  has  been  done  by 
geologists  in  regard  to  relative  time  ;  but  this  can  be 
of  no  service  to  us  in  our  present  inquiry.  Unfortu- 
nately very  little  trustworthy  work  has  been  done  in 
the  way  of  determining  the  absolute  length  of  geo- 
logical periods.  Happily,  however,  great  exactness  of 
measure  is  not  required.  A  rough  approximation  to 
the  truth  will  suffice  for  our  present  purpose.  If 
it  can  be  shown  to  be  more  than  fifteen  or  twenty 
millions  of  years  since  life  first  appeared  on  the  earth, 


AGE  OF  THE  SUN'S  HEAT  89 

it  will  as  effectually  prove  that  gravitation  alone  could 
not  have  been  the  source  from  which  the  sun  derived 
his  heat  as  if  it  were  shown  that  that  period  was  a 
thousand  times  more  remote.  All  we  have  to  do  is 
simply  to  assign  an  inferior  limit  to  the  age  of  life  on 
the  earth ;  and  this  can  be  effectually  done  by  means 
of  the  methods,  imperfect  though  they  be,  which  we 
have  at  command.  As  the  question  of  geological  time 
is  of  some  importance  in  relation  to  our  present 
inquiry,  I  shall  consider  it  at  some  length. 

Testimony  of  Geology  :  method  employed. — What 
has  subsequently  proved  to  be  a  pretty  successful 
method  of  measuring  geological  time  suggested  itself 
to  my  mind  during  the  summer  of  1865.  It  then 
occurred  to  me  that  we  might  obtain  a  tolerably 
accurate  measure  of  absolute  geological  time  from 
the  present  rate  of  subaerial  denudation,  which  might 
be  ascertained  in  the  following  way :  The  rate  of 
subaerial  denudation  must  be  equal  to  the  rate  at 
which  materials  are  carried  off  the  land  into  the  sea  ; 
and  this  is  measured  by  the  rate  at  which  sediment  is 
carried  down  by  our  river  systems.  Consequently,  in 
order  to  determine  the  present  rate  of  subaerial  denuda- 
tion, we  have  only  to  ascertain  the  quantity  of  sediment 
annually  carried  down  by  the  river  systems.  This  gives 
us  the  time  required  to  remove  any  given  quantity, 
say  one  foot,  off  the  face  of  the  country.  If  we 
assume  the  rate  to  be  pretty  much  the  same  during 
past  geological  ages,  we  have  a  means^  of  telling  the 
time  that  was  occupied  in  removing  any  known  thick- 
ness of  strata.  But  as  we  never  can  be  perfectly 


40  STELLAR  EVOLUTION 

certain  that  the  rate  is  the  same  in  both  cases,  the 
results  can,  of  course,  be  regarded  as  only  approxi- 
mately true. 

Taking  the  quantity  of  sediment  discharged  into 
the  sea  annually  by  the  Mississippi  river,  as  deter- 
mined by  Messrs.  Brown  and  Dickson,1  I  found  that 
it  amounted  to  one  foot  off  the  face  of  the  country 
in  1,388  years,  and  that,  at  this  rate  of  denudation, 
our  continents,  even  if  they  had  an  elevation  of 
1,000  feet,  would  not  remain  above  sea-level  over 
1,500,000  years.2  This  was  an  exaggerated  estimate 
of  the  quantity  of  sediment,  for  I  shortly  afterwards 
found  that  far  more  accurate  determinations  were 
made  by  Messrs.  Humphreys  and  Abbot,3  who  were 
employed  by  the  United  States  Government  to  report 
upon  the  physics  and  hydraulics  of  the  Mississippi. 
Messrs.  Brown  and  Dickson  had  estimated  the  quantity 
of  sediment  at  28,188,083,892  cubic  feet,  whereas 
Messrs.  Humphreys  and  Abbot  found  it  to  be  only 
6,724,000,000  cubic  feet,  or  less  than  one-fourth  that 
amount.  This  gives  one  foot  in  6,000  years  as  the 
rate  of  denudation. 

1  Proceedings  of  tlie  American  Association  for  the  Advancement 
of  Science  for  1848. 

2  Philosophical  Magazine,  February  1867.    I  was  not  aware  at 
this  time  that  Mr.  Alfred  Tylor  had  previously  applied  the  same 
method  to  determine  an  entirely  different  point,  viz.:  how  much  the 
sea-level  is  being  raised  by  the  sediment  deposited  on  the  sea-bottom. 
Mr.  Tylor's  paper,  entitled  "  On  Changes  of  the  Sea-Level  effected 
by  existing  Physical  Causes  during  stated  Periods  of  Time,"  appeared 
in  the  Phil.  Mag.  for  April  1853.     Mr.  Tylor  came  to  the  conclusion 
that  the  sea-level  was  being  raised,  from  this  cause,  about  3  inches 
in  10,000  years. 

1  Report  upon  the  Physics  and  Hydraulics  of  the  Mississippi, 


AGE  OF  THE  SUN'S  HEAT 


41 


At  this  time  Dr.  Archibald  Geikie  took  up  the 
question  and  went  into  the  consideration  of  the  sub- 
ject in  a  most  thorough  manner ;  and  it  is  mainly 
through  the  instrumentality  of  his  writings  on  the 
matter l  that  the  method  under  consideration  has 
gained  such  wide-spread  acceptance  among  geologists. 
After  an  examination  of  nearly  all  that  is  known  re- 
garding the  amount  of  sediment  carried  down  by 
rivers,  he  drew  up  the  following  table,  showing  the 
number  of  years  required  by  seven  rivers  to  remove 
one  foot  of  rock  from  the  general  surface  of  their 
basins. 


Danube 

Mississippi 

Nith     . 

Ganges 

Rhone 

Hoang-Ho 

Po 


Mean 


6,846  years 

6,000  „ 

4,723  „ 

2,358  „ 

1,528  „ 

1,464  „ 

729  „ 

3,378 


This  gives  a  mean  of  3,378  years  to  remove  one 
foot,  or  a  little  over  one-half  the  time  taken  by  the 
Mississippi.  This  mean  appears  to  be  generally 
taken  as  representing  the  average  rate  of  subaerial 
denudation  of  the  whole  earth,  but  it  has,  I  fear,  been 
rather  too  hastily  adopted.  To  estimate  correctly  the 
quantity  of  sediment  annually  discharged  by  a  large 
river  is  a  most  difficult  and  laborious  undertaking. 
A  perusal  of  the  voluminous  report  of  Messrs.  Hum- 
phreys and  Abbot,  extending  over  690  pages,  which 


1  Trans,  of  Geol.  Soc.  of  Glasgow,  vol.  iii. ;  Jukes  &  Geikie's 
Manual  of  Geology,  chap.  xxv. ;  Text  Book  of  Geology,  p.  441. 


42  STELLAR  EVOLUTION 

Dr.  Geikie  justly  styles  a  model  of  patient  and  ex- 
haustive research,  will  clearly  show  this,  and  at  the 
same  time  prove  how  skilfully  and  accurately  the  task 
allotted  to  them  was  performed. 

The  risk  of  making  very  serious  errors  in  comput- 
ing the  amount  of  sediment  discharged,  unless  proper 
precautions  are  taken,  is  well  illustrated  in  the  case 
of  the  determinations  made  by  Messrs.  Brown  and 
Dickson,  to  which  reference  has  already  been  made. 
Although  their  report  shows  that  they  took  great 
pains  in  order  to  arrive  at  correct  results — in  fact, 
they  computed  the  total  annual  quantity  of  sediment 
discharged  to  within  a  cubic  foot — after  all,  in- 
stead of  being  correct  to  this  minute  quantity,  they 
gave  a  total  more  than  fourfold  what  it  ought  to  be. 
A  somewhat  similar  discrepancy  exists  in  reference  to 
the  denudation  of  the  basin  of  the  Ganges.  The  time 
required  to  lower  its  surface  by  one  foot  is,  according 
to  one  estimate,  2,358  years ;  according  to  another, 
1,751 ;  and  according  to  a  third,  only  1,146  years. 
The  first  figure  is  probably  nearest  the  truth.  Still, 
these  differences  show  both  the  difficulty  of  the  pro- 
blem and  the  necessity  of  caution  in  adopting  any 
of  these  results  as  correct. 

By  far  the  most  trustworthy  determinations  of  the 
whole  are  those  of  the  Mississippi  by  Messrs.  Hum- 
phreys and  Abbot,  which  may  be  relied  upon  as  not  far 
from  the  truth.  But,  supposing  the  estimates  in  the 
foregoing  table  to  be  perfectly  correct,  can  we  assume 
that  their  mean  may  be  safely  taken  as  probably  re- 
presenting the  average  rate  of  denudation  of  the  whole 


AGE   OF  THE  SUN'S   HEAT  43 

earth  ?  I  would  most  unhesitatingly  reply,  Certainly 
not.  The  Ehone  and  Po  are  full  of  glacier  mud 
from  the  Alps ;  and  the  amount  of  sediment  which 
they  carry  down  may  give  us  the  rate  of  denudation 
of  Switzerland,  but  certainly  not  that  of  the  whole 
earth,  or  even  of  Europe.  The  same  may  be  said  of 
the  Ganges,  which  is  charged  with  the  mud  which  it 
brings  down  from  the  Himalaya  Mountains.  The 
Hoang-Ho,  or  Yellow  Eiver,  is  an  exceptionally  muddy 
river ;  in  fact,  it  derives  its  name  from  the  vast  quan- 
tity of  yellow  mud  held  by  its  waters  in  a  state  of 
solution.  It  was  probably  the  exceptionally  muddy 
character  of  the  Po,  the  Ehone,  the  Ganges,  and  the 
Yellow  Eiver  which  attracted  attention,  and  led  to 
observations  being  made  of  the  sediment  they  contain. 
Eivers  more  unsuitable  than  these  to  give  us  the 
average  denudation  of  the  earth's  surface  could  not 
well  be  selected.  Among  the  seven  rivers  in  the  table, 
leaving  out  of  account  the  small  Scottish  stream,  the 
Nith,  with  its  basin  of  only  200  square  miles,  there  are 
only  two,  the  Mississippi  and  the  Danube,  that  drain 
countries  which  may  be  regarded  as  in  every  way 
resembling  the  average  condition  of  the  earth's  sur- 
face. I  would  choose  the  Mississippi  as  being  supe- 
rior to  the  Danube,  for  two  reasons :  (1)  because 
the  rate  of  denudation  of  its  basin  has  been  more 
accurately  determined;  and  (2)  because  the  area  of 
its  basin  not  only  exceeds  that  of  the  Danube  as  five  to 
one,  but  better  fulfils  the  necessary  conditions,  as  Sir 
Charles  Lyell  has  so  clearly  shown.  "  That  river," 
says  Sir  Charles,  "  drains  a  country  equal  to  more 


44  STELLAE  EVOLUTION 

than  half  the  continent  of  Europe,  extends  through 
twenty  degrees  of  latitude,  and  therefore  through 
regions  enjoying  a  great  variety  of  climate,  and  some 
of  its  tributaries  descend  from  mountains  of  great 
height.  The  Mississippi  is  also  more  likely  to  afford 
us  a  fair  test  of  ordinary  denudation,  because,  unlike 
the  St.  Lawrence  and  its  tributaries,  there  are  no 
great  lakes  in  which  the  fluviatile  sediment  is  thrown 
down  and  arrested  on  its  way  to  the  sea."  1  There  is 
no  other  river  in  the  globe  which  to  my  mind  better 
fulfils  the  required  conditions.  It  is  no  doubt  true 
that  the  rate  of  denudation  of  the  basin  of  the  Missis- 
sippi is  probably  less  than  that  of  Switzerland,  Nor- 
way, and  the  Himalayas,  where  glaciers  abound,  and 
certainly  less  than  that  of  Greenland  and  the  Ant- 
arctic continent ;  but,  on  the  other  hand,  this  rate  is 
certainly  much  greater  than  that  of  the  whole  con- 
tinent of  Africa,  Australia,  and  large  tracts  of  Asia, 
where  the  rainfall  is  much  smaller.  One  foot  in 
6,000  years  may,  therefore,  I  think,  be  safely  taken 
as  the  average  rate  of  denudation  of  the  whole  surface 
of  the  globe. 

The  average  rate  of  denudation  in  the  past  pro- 
bably not  much  greater  than  in  the  present. — The  belief 
has  long  prevailed  that  the  rate  of  denudation  was 
much  greater  in  past  ages  than  it  is  now ;  but  I  am 
unable  to  perceive  any  good  grounds  for  concluding 
that  such  was  the  case  at  any  time  since  the  begin- 
ning of  the  Palaeozoic  period.  Various  reasons  have, 
however,  been  assigned  for  this  supposed  greater  rate ; 

1  Student's  Elements  of  Geology,  p.  91. 


AGE   OF  THE  SUN'S  HEAT  45 

and  to  the  consideration  of  these  I  shall  now  very 
briefly  refer. 

It  has  been  thought  that  at  some  remote  epoch  of 
the  earth's  history,  when  the  moon  was  much  nearer 
and  the  day  much  shorter  than  now,  the  rate  of  de- 
nudation would,  owing  to  the  erosive  power  of  the 
enormous  tides  which  would  then  prevail,  be  much 
greater  than  at  the  present  day.  This,  however,  is 
very  doubtful.  There  is  nothing  in  the  stratified 
rocks  which  affords  any  support  to  the  idea  of  great 
tidal  waves  having  swept  over  the  land,  at  least 
since  the  time  when  life  began  on  our  globe.  Such  a 
state  of  things  would  have  destroyed  all  animal  life. 
"  The  Palaeozoic  sediments,"  as  Professor  A.  Winchell 
remarks,  "  have  been  deposited,  for  the  chief  part,  in 
quiet  seas.  The  deep  beds  of  limestones  and  shales 
are  spread  out  in  sheets  continent-wide,  which  testify 
unmistakably  to  placid  waters  and  slow  deposition."  l 
But  high  tides,  not  sweeping  over  the  land,  would 
not  increase  the  rate  of  denudation  to  the  extent  sup- 
posed. High  tides  silt  up  a  river  channel  more  readily 
than  they  deepen  it.  A  higher  tide  would  probably 
produce  a  greater  destruction  of  sea-coast :  it  would 
tend  to  increase  the  rate  of  marine  denudation,  but 
this  would  not  materially  affect  the  general  rate  of 
denudation.  For,  as  the  present  rate  of  marine  de- 
nudation is  to  that  of  subaerial  denudation  only  as 
1  to  about  1,700,2  it  would  take  a  very  large  increase 
in  the  rate  of  marine  denudation  to  affect  sensibly  the 
general  result.  Suppose  the  rate  of  marine  denuda- 

1  World  Life,  p.  265.  2  See  Climate  and  Time,  p.  337. 


46  STELLAE  EVOLUTION 

tion  to  have  been,  for  example,  ten  times  as  great 
during  the  Palaeozoic  age  as  it  is  now  (which  it  cer- 
tainly was  not),  it  would  only  have  shortened  the 
time  required  to  effect  a  given  amount  of  denudation 
of  the  whole  earth  by  9  years  in  1,700,  i.e.  by  little 
more  than  one-half  per  cent. 

Again,  it  is  assumed  that  the  greater  rate  of 
terrestrial  rotation  in  the  early  ages  would  produce 
certain  influences  which  would  in  turn  bring  about  a 
greater  amount  of  denudation.  The  rate  of  rotation 
has  been  slowly  decreasing  for  ages,  and  in  Palaeozoic 
times  it  must,  of  course,  have  been  greater  than  at 
present.  A  more  rapid  rotation  would  increase  the 
velocity  of  the  trade  and  anti-trade  winds,  and  would 
thus  tend  to  augment  the  action  of  those  meteoro- 
logical agents  chiefly  effective  in  the  work  of  subaerial 
denudation.  Here  again  the  testimony  of  geology  is 
negative.  We  have  no  geological  grounds  to  conclude 
that  the  winds  of  Palaeozoic  times  were  stronger  than 
those  at  the  present  day.  The  heat  was  no  doubt 
greater,  and  perhaps  there  was  more  rain;  but,  on 
the  other  hand,  there  would  be  less  frost,  snow,  ice, 
and  other  denuding  agents. 

There  is  one  cause  which  would,  perhaps,  be  more 
effective  than  any  of  the  foregoing  :  viz.  the  periodic 
occurrence  of  glacial  epochs.  When  a  country  is 
buried  under  ice,  the  erosion  of  the  surface  is  great. 
But  it  must  be  borne  in  mind  that  the  influence  of 
rain,  rivers,  and  other  denuding  agents  now  in  opera- 
tion would  then,  in  the  glaciated  regions,  be  almost 
nil.  Besides,  the  greater  part  ©f  the  materials  ground 


AGE  OF  THE  SUN'S  HEAT  47 

off  the  rocks  would  be  left  on  the  land ;  and,  when  the 
ice  disappeared,  it  would  be  found  in  the  form  of  a 
thick  mantle  of  boulder  clay — a  mantle  which  would 
protect  the  rocky  surface  of  the  country  for  thousands 
and  tens  of  thousands  of  years  from  further  denuda- 
tion. This  is  shown  by  the  fine  striae  on  the  rocky 
surface,  made  perhaps  more  than  50,000  years  ago, 
remaining  under  the  boulder  clay  as  perfect  as  the  day 
on  which  they  were  engraved.  But,  more  than  all 
this,  a  very  considerable  part  of  the  1  foot  presently 
being  removed  off  the  country  in  6,000  years  consists 
of  the  loose  materials  belonging  to  the  glacial  epoch, 
such  as  sands,  gravels,  and  boulder  clay,  which  are 
being  swept  off  the  surface  by  rain  and  river  action. 
Were  it  not  for  this,  the  present  rate  of  subaerial 
denudation  would  not  be  so  high  as  it  actually  is. 
Taking  all  things  into  consideration,  it  is,  I  think, 
obvious  that  the  average  rate  of  denudation  since  the 
beginning  of  Palaeozoic  times  was  probably  not  much 
greater  than  at  the  present  day. 

How  the  method  has  been  applied. — Having  deter- 
mined what  appears  to  be  the  probable  average  rate 
of  subaerial  denudation,  we  may  now  proceed  to  con- 
sider the  way  in  which  this  rate  has  been  applied  to 
measure  past  geological  time.  There  are  two  ways  in 
which  it  may  be  applied  for  this  purpose.  It  may  (1) 
be  applied  directly :  knowing  the  thickness  of  strata 
which  may  have  been  removed  by  denudation,  we  can 
easily  tell,  from  that  rate,  the  time  it  required  to  effect 
their  removal.  If  we  have  evidence,  for  example,  that 
at  some  epoch  1,000  feet  of  stratified  rock  were 


48  STELLAR  EVOLUTION 

carried  away,  then,  on  the  assumption  that  the  rate  of 
denudation  was  the  same  at  that  epoch  as  now,  we 
have  1,000  x  6,000  =  6,000,000  years  as  the  re- 
quired time.  (2)  It  may  be  applied  indirectly : 
knowing  the  thickness  of  the  strata,  we  may  estimate 
the  time  required  for  their  formation.  This  is  the 
way  in  which  it  has  usually  been  applied,  but,  as  we 
shall  see,  it  is  the  less  satisfactory  way  of  the  two. 

Dr.  A.  Geikie  gives  the  land  area  of  the  globe 
as  52,000,000  square  miles,  and  that  of  water  as 
144,712,000  square  miles.1  We  may  thus  take  the 
proportion  of  land  to  water  roughly  as  1  to  3 ;  about 
one-quarter  of  the  earth's  surface  being  land,  and 
three-quarters  water.  One  foot,  therefore,  removed 
off  the  surface  of  the  land  would  cover  the  whole 
globe  with  a  layer  3  inches  thick,  or  the  entire  sea- 
bottom  with  a  layer  4  inches  thick. 

If  we  knew  the  total  quantity  of  stratified  rock 
on  the  globe,  we  could  easily  tell  the  time  that 
would  be  required  for  its  formation.  Most  geologists 
would,  I  believe,  be  inclined  to  admit  that,  if  spread 
uniformly  over  the  entire  globe,  it  would  form  a  layer 
of  at  least  1,000  feet  in  thickness.  In  such  a  case 
the  time  required  for  its  deposition  would  be  as 
follows  : 

1,000  x  6,000  x  4  =.24,000,000  years. 

This  would  not,  however,  represent  the  age  of  the 
stratified  rocks.  It  would  only  represent  the  time 
required  to  deposit  the  rocks  which  we  have  assumed 

1  Physical  Geography,  p.  103. 


AGE  OF  THE  SUN'S  HEAT  49 

to  be  now  in  existence.  The  greater  mass  of  sedi- 
mentary rocks  has  been  formed  out  of  previously 
existing  sedimentary  rocks,  and  these  again  out  of 
sedimentary  rocks  still  older.  The  oldest  known 
sedimentary  rocks  are  the  Laurentian;  but  these 
are  believed  by  geologists  to  have  been  formed  from 
still  older  sedimentary  rocks.  It  is  therefore  evident 
that  the  materials  composing  our  stratified  beds 
must  have  passed  through  many  cycles  of  destruc- 
tion and  re-formation.  The  materials  of  some  of 
the  recent  formations,  for  example,  may  have  passed 
through  denudation  and  deposition  a  dozen  of  times 
over.1  The  time  required  to  have  deposited  at  a 
given  rate  the  present  existing  mass  of  sedimentary 
rocks  is  probably  but  a  small  fraction  of  the  time 
required  to  have  deposited  at  the  same  rate  the  total 
mass  that  has  actually  been  formed.  Few  geologists, 
I  think,  who  will  duly  reflect  on  the  subject,  will  deem 
it  too  much  to  say  that  the  present  existing  stratified 
rocks  have  on  an  average  passed  at  least  thrice 
through  the  cycle  of  destruction  and  re-formation.  If 
this  be  admitted,  then  the  1,000  feet  of  stratified 
rock  represent,  not  a  period  of  24,000,000  years,  but 
a  period  three  times  as  great,  viz.  72,000,000  years. 

It  is  impossible  to  tell  from  geological  data  the 
actual   age  of  the   stratified  rocks ;  but  this  is  not 

1  It  is  this  destruction  of  the  stratified  rocks  which  makes  it  so 
difficult  to  detect  the  marks  of  former  glacial  epochs,  and  which  has 
led  to  such  prevailing  misconceptions  regarding  the  evidence  which 
we  ought  to  expect  of  those  epochs.  See  paper  read  before  the 
Geological  Society,  "  On  Prevailing  Misconceptions  regarding  the 
Evidence  which  we  ought  to  expect  of  former  Glacial  Periods,'1 
January  23,  1889. 
6 


50  STELLAR  EVOLUTION 

required.  What  we  require  is,  as  already  stated,  not 
their  actual  age,  but  an  inferior  limit  to  that  age. 

Method  as  applied  by  Professor  Haughton. — Pro- 
fessor Haughton  estimates  the  mass  of  the  stratified 
rocks  down  to  the  time  of  the  Miocene  Tertiary  period 
as  being  177,200  feet  in  thickness,  and  covering  an 
area  equal  to  that  of  the  sea.  The  present  rate  of 
subaerial  denudation  he  considers  to  be  equal  to  one 
foot  removed  off  the  surface  of  the  land  in  3,090  years. 
If  the  proportion  of  land  to  water  be  taken  as  52  to 
145,  it  thus  requires  8,616  years  to  deposit  one  foot 
of  sediment  over  the  bed  of  the  ocean,  and  conse- 
quently this  is  the  rate  at  which  strata  are  at  present 
being  formed.  This  would  give  8,616  x  177,200 
=  1,526,750,000  years  for  the  age  of  the  stratified 
rocks.  But  he  assumes  the  rate  of  denudation  to 
have  been  ten  times  greater  in  geological  time  than 
at  present.  This  consequently  reduces  the  age  of 
the  rocks  to  152,675,000  years.  By  adding  one-third 
for  the  time  which  has  elapsed  since  the  Miocene 
Tertiary  period  he  gets  200,000,000  years  as  a 
minimum  length  of  geological  time.1 

The  validity  of  this  result  rests  upon  what  appear 
to  me  to  be  two  very  doubtful  assumptions.  It  is 
assumed  in  his  calculations  that  the  total  amount 
of  strata  formed  during  past  ages  (not  the  amount 
presently  remaining)  was  equal  to  a  mass  177,200 
feet  in  thickness,  covering  the  entire  area  of  the 
ocean.  This  is  certainly  doubtful.  It  may  have 
been  as  great,  for  anything  that  can  be  proved  to  th§ 

1  Physical  Geography,  p.  94. 


AGE  OF  THE  SUN'S  HEAT  51 

contrary;  but  we  have  no  evidence  that  it  was  so. 
Certainly  there  is  no  evidence  that  the  rate  of 
subaerial  denudation  during  past  ages  was  ever  ten 
times  as  great  as  it  is  now.  But  how  is  a  length  of 
200,000,000  years  to  be  reconciled  with  the  age  of 
the  sun's  heat  ?  The  stratified  rocks  may  be  as  old 
as  this,  but  assuredly  they  are  not  if  gravitation  was 
the  only  source  from  which  the  sun  derived  his 
energy. 

Method  as  applied  by  Mr.  Alfred  R.  Wallace. — 
Mr.  Wallace  adopts  Professor  Haughton's  estimate 
of  177,200  feet  for  the  maximum  thickness  of  the 
sedimentary  rocks.  But,  instead  of  supposing,  like 
Professor  Haughton,  the  products  of  denudation  to 
be  uniformly  spread  over  the  entire  sea-bottom,  he 
supposes  them  spread  over  a  belt  of  merely  30 
miles  broad,  extending  along  the  entire  coast-line  of 
the  globe,  which  he  estimates  at  100,000  miles. 
This  gives  an  area  of  3,000,000  square  miles  on 
which  the  denuded  matter  of  the  whole  land  area  of 
57,000,000  square  miles  is  deposited.  These  two 
areas  are  to  one  another  as  1  to  19,  and  thus  it 
follows  that  deposition  goes  on  19  times  as  fast 
as  denudation.  The  rate  of  denudation  he  takes  as 
one  foot  removed  off  the  surface  of  the  land  in  3,000 
years,  so  that  the  rate  of  deposition  would  be  about 
one  foot  in  158  years,  and  consequently  the  time 
required  to  deposit  the  177,200  feet  of  rock  would  be 

177,200  x  158  =  27,997,600  years. 
This  is  a  period  double  what  the  gravitation  theory 


52  STELLAE  EVOLUTION 

of  the  source  of  the  sun's  energy  can  afford.  And  if 
the  rate  of  denudation  be  taken  at  one  foot  in  6,000 
years,  which  is,  as  we  have  seen,  probably  nearer  the 
truth,  then  this  would  make  the  age  of  the  stratified 
rocks  56,000,000  years. 

There  seems  to  be  a  little  ambiguity  about  Mr. 
Wallace's  result.  Do  the  177,200  feet  represent  the 
quantity  of  rock  which  presently  exists,  or  do  they 
represent  the  total  quantity  which  has  been  formed 
during  all  past  ages?  If  the  former,  then  the 
28,000,000  years  are  but  a  fraction  of  the  time 
which  must  have  been  required ;  for,  as  we  have 
been  shown,  the  materials  composing  the  stratified 
rocks  have,  on  an  average,  been  deposited  at  least 
three  or  four  times  over.  If,  on  the  other  hand,  the 
thickness  is  meant  to  represent  the  total  quantity  of 
rock  which  has  been  formed  during  the  whole  of  past 
geological  time,  then  the  question  arises,  by  what 
means  could  this  quantity  possibly  be  ascertained  ? 
In  other  words,  how  was  the  relation  between  the 
present  quantity  and  the  total  quantity  ascertained  ? 
But  in  either  case  the  result  is  wholly  irreconcilable 
with  the  gravitation  theory  of  the  source  of  the  sun's 
heat. 

Method  as  applied  directly. — We  have  seen  that  it 
is  impossible  to  determine  the  actual  age  of  the  earth 
from  the  stratified  rocks,  even  if  we  knew  with  perfect 
accuracy  their  present  total  amount.  We  have  also 
seen  that  from  the  rate  of  deposition  we  cannot  fix 
with  any  degree  of  certainty  a  minimum  value  for  the 
age  of  these  rocks.  We  can,  however,  by  means  of 


AGE  OF  THE  SUN'S  HEAT  53 

the  first  or  direct  application  of  the  method,  assign 
with  tolerable  accuracy,  as  was  shown  on  a  former 
occasion,1  a  minimum  age  to  the  earth.  We  can  be 
far  more  certain  of  the  time  which  must  have  been 
required  to  remove  by  denudation,  say,  a  thousand 
feet  of  rock  than  we  can  possibly  be  of  the  time  re- 
quired to  have  deposited  a  thousand  feet  of  sediment. 
The  thousand  feet  of  sediment  may,  under  certain 
conditions,  have  been  deposited  in  a  hundred  years, 
while  under  other  conditions  they  may  have  required 
a  million  of  years.  In  fact,  nothing  can  be  more  un- 
certain than  the  rate  of  deposition  :  it  depends  upon 
such  a  multitude  of  circumstances.  At  the  mouth  of 
a  great  river,  for  example,  a  foot  of  sediment  may  be 
deposited  in  a  single  day,  whereas  in  some  places,  as 
in  mid-ocean,  it  may  require  a  million  of  years  to  de- 
posit the  same  amount.  But  in  reference  to  subaerial 
denudation  no  such  uncertainty  exists. 

The  utter  inadequacy  of  a  period  of  20,000,000 
years  for  the  age  of  our  earth  is  demonstrable  from 
the  enormous  thickness  of  rock  which  is  known  to 
have  been  removed  off  certain  areas  by  denudation. 
I  shall  now  briefly  refer  to  a  few  of  the  many  facts 
which  might  be  adduced  on  this  point. 

Evidence  from  "faults" — One  plain  and  obvious 
method  of  showing  the  great  extent  to  which  the 
general  surface  of  the  country  has  been  lowered  by 
denudation  is  furnished,  as  is  well  known,  by  the  way 
in  which  the  inequalities  of  surface  produced  by  faults 

1  Quart.  Journ.  of  Science,  July  1877 ;  Climate  and  Cosmology, 
chap.  xvii. 


54  STELLAR  EVOLUTION 

or  dislocations  have  been  effaced.  It  is  quite  common 
to  meet  with  faults  where  the  strata  on  the  one  side 
have  been  depressed  several  hundreds — and  in  some 
cases  thousands — of  feet  below  those  on  the  other ; 
but  we  seldom  find  any  indications  of  such  on  the 
surface,  the  inequalities  on  the  surface  having  been 
all  removed  by  denudation.  Now,  in  order  to  effect 
this,  a  mass  of  rock  must  have  been  removed  equal  in 
thickness  to  the  extent  of  the  dislocation.  The  fol- 
lowing are  a  few  examples  of  large  faults : 

The  great  Irwell  fault,  described  by  Professor  Hull,1 
which  stretches  from  the  Mersey  west  of  Stockport  to 
the  north  of  Bolton,  has  a  throw  of  upwards  of  3,000 
feet. 

Some  remarkable  faults  have  been  found  by  Pro- 
fessor Kamsay  in  North  Wales.  For  example,  near 
Snowdon,  and  about  a  mile  E.S.E.  of  Beddgelert, 
there  is  a  fault  with  a  downthrow  of  5,000  feet ;  and 
in  the  Berwyn  Hills,  between  Bryn-mawr  and  Post- 
gwyn,  there  is  one  of  5,000  feet.  In  the  Aran  Eange 
there  is  a  great  fault,  designated  the  Bala  fault,  with 
a  downthrow  of  7,000  feet.  Again,  between  Aran 
Mowddwy  and  Careg  Aderyn  the  displacement  of  the 
strata  amounts  to  no  less  than  from  10,000  to  11,000 
feet.2  Here  we  have  evidence  that  a  mass  of  rock, 
varying  from  one  to  two  miles  in  vertical  thickness, 
must  have  been  denuded  in  many  places  from  the 
surface  of  the  country  in  North  Wales. 

The  fault  which  passes  along  the  east  side  of  the 

1  Mem  GeoL  Survey  of  Lancashire,  1862. 
s  Mem.  GeoL  Survey  of  Great  Britain,  vol.  iii. 


AGE   OF  THE  SUN'S  HEAT  55 

Pentlands  is  estimated  to  have  a  throw  of  upwards  of 
8,000  feet.1  Along  the  flank  of  the  Grampians  a  great 
fault  runs  from  the  North  Sea  at  Stonehaven  to  the 
estuary  of  the  Clyde,  throwing  the  Old  Eed  Sandstone 
on  end  sometimes  for  a  distance  of  two  miles  from  the 
line  of  dislocation.  The  amount  of  the  displacement, 
Dr.  A.  Geikie 2  concludes,  must  in  some  places  be  not 
less  than  5,000  feet,  as  indicated  by  the  position  of 
occasional  outliers  of  conglomerate  on  the  Highland 
side  of  the  fault. 

The  great  fault  crossing  Scotland  from  near  Dunbar 
to  the  Ayrshire  coast,  which  separates  the  Silurians 
of  the  South  of  Scotland  from  the  Old  Bed  Sandstone 
and  Carboniferous  tracts  of  the  North,  has  been  found 
by  Mr.  B.  N.  Peach,  of  the  Geological  Survey,3  to 
have  in  some  places  a  throw  of  fully  15,000  feet. 
This  great  dislocation  is  older  than  the  Carboniferous 
period,  as  is  shown  by  the  entire  absence  of  any  Old 
Bed  Sandstone  on  the  south  side  of  the  fault,  and  by 
the  occurrence  of  the  Carboniferous  Limestone  and 
Coal-measures  lying  directly  on  the  Silurian  rocks. 
We  obtain  here  some  idea  of  the  enormous  amount  of 
denudation  which  must  have  taken  place  during  a 
comparatively  limited  geological  epoch.  So  vast  a 
thickness  of  Old  Bed  Sandstone  could  not,  as  Mr. 
Peach  remarks,  "  have  ended  originally  where  the 
fault  now  is,  but  must  have  swept  southwards  over 
the  Lower  Silurian  uplands.  Yet  these  thousands  of 

1  Memoir  to  Sheet  32,  Geol.  Survey  Map  of  Scotland. 

»  Nature,  vol.  xiii.  p.  390. 

•  Explanation  to  Sheet  15,  Geol.  Survey  Map  of  Scotland. 


56  STELLAE  EVOLUTION 

feet  of  sandstones,  conglomerates,  lavas,  and  tuffs 
were  so  completely  removed  from  the  south  side  of 
the  fault  previous  to  the  deposition  of  the  Car- 
boniferous Limestone  series  and  the  Coal-measures, 
that  not  a  fragment  of  them  is  anywhere  to  be 
seen  between  these  latter  formations  and  the  old 
Silurian  floor."1  This  enormous  thickness  of  nearly 
three  miles  of  Old  Eed  Sandstone  must  have  been 
carried  away  during  the  period  which  intervened 
between  the  deposition  of  the  lower  members  of  the 
Lower  Old  Eed  Sandstone  and  the  accumulation  of 
the  Carboniferous  Limestone. 

Near  Tipperary,  in  the  south  of  Ireland,  there  is  a 
dislocation  of  the  strata  of  not  less  than  4,000  feet,2 
which  brings  down  the  Coal-measures  against  the 
Silurian  rocks.  Here  1,000  feet  of  Old  Eed  Sandstone, 
3,000  feet  of  Carboniferous  Limestone,  and  800  feet 
of  Coal-measures  have  been  removed  by  denudation 
off  the  Silurian  rocks.  Not  only  has  this  immense 
thickness  of  beds  been  carried  away,  but  the  Silurian 
itself  on  which  they  rested  has  been  eaten  down  in  some 
places  into  deep  valleys  several  hundreds  of  feet  below 
the  surface  on  which  the  Old  Eed  Sandstone  rested. 

1  I  have  been  informed  by  Mr.  Peach  that  since  the  above  was 
written  additional  light  has  been  cast  on  this  immense  fault.    It  has 
been  found,  he  says,  that  the  fault   consists  of  two  sub-parallel 
branches,  the  more  southerly   of  which  has  the  effect  of  bringing 
the  rocks  of  the  Upper  Silurian  age  against  the  Lower  Silurian  beds. 
The  northern  branch  brings  the  upper  division  of  the  Lower  Old  Eed 
Sandstones,  in  turn,  against  the  Upper  Silurian  rocks.     This,  Mr. 
Peach  remarks,  does  not  in  the  least  invalidate  the  reasoning  as  to 
the  amount  of  material  removed  by  denudation  from  this  region  in 
the  time  specified.    In  fact,  it  shows,  he  says,  that  a  greater  amount 
must  have  been  removed  than  was  at  first  suspected. 

2  Jukes's  and  Geikie's  Manual  of  Geology,  p.  441. 


AGE  OF  THE  SUN'S  HEAT  57 

Turning  to  the  American  continent,  we  find  the 
amount  of  rock  removed  to  be  even  still  greater.  In 
the  Valley  of  Thessolon,  to  the  north  of  Lake  Huron, 
there  is  a  dislocation  of  the  strata  to  the  extent  of 
9,000  feet.1 

In  front  of  the  Chilowee  Mountains  there  is  a 
vertical  displacement  of  the  strata  of  more  than 
10,000  feet.2  Professor  H.  D.  Eogers  found  in  tho 
Appalachian  coal-fields  faults  ranging  from  5,000  feet 
to  more  than  10,000  feet  of  displacement. 

In  the  Nova  Scotia  coal-fields  one  or  two  miles 
in  thickness  of  strata  have  been  removed  in  some 
places.3 

A  great  fracture  runs  along  the  axis  of  the  Sierra 
Nevada  for  300  miles,  accompanied  by  a  dislocation 
of  3,000  to  10,000  feet.4 

The  anticlinal  of  the  Park  Kange  of  the  Kocky 
Mountains  was  cleft  down  the  axis,  and  the  eastern 
half  depressed  10,000  feet.  And  Mr.  J.  P.  Lesley 
gives  an  account  of  a  fault  in  the  Appalachians  of  not 
less  than  20,000  feet,  bringing  the  upper  Devonian 
strata  on  the  one  side  opposite  to  the  lowest  Cambrian 
on  the  other.5 

A  fault  with  a  vertical  displacement  of  20,000  feet 
was  found  in  the  Uinta  Mountains.6 

In  the  Aqui  range  of  mountains,  Utah,  there  is  a 

1  Geology  of  Canada,  1863,  p.  61. 

8  Safford's  Geology  of  Tennessee,  p.  309. 

3  LyelPs  Student's  Manual,  chap,  xxiii. 

4  Geological  Studies,  by  Prof.  A.  Winchell,  p.  165. 

5  Geological  Studies,  pp.  93,  163. 

a  Powell's  Geology  of  the  Uinta  Mountains. 


58  STELLAR  EVOLUTION 

fault  determined  by  Mr.  S.  F.  Emmons  to  be  at  least 
10,000  feet.1 

The  Grand  Canon  of  Colorado,  in  some  places 
4,000,  5,000,  and  6,000  feet  in  depth,  is  cut,  says  Pro- 
fessor A.  Winchell,  in  a  plateau  which  has  itself  been 
lowered  by  erosion  to  the  extent  of  10,000  feet ;  and 
this  plateau  occupies  an  area  of  13,000  to  15,000 
square  miles.2 

The  Grand  "  Wash  Fault,"  Colorado,  has  a  down- 
throw to  the  west  of  6,000  feet.  The  "Hurricane 
Fault,"  close  to  it,  has  displaced  the  strata  to  the  ex- 
tent of  over  12,000  feet.3 

In  the  Valley  of  East  Tennessee,  Appalachian 
Mountains,  it  has  been  shown  by  Mr.  J.  P.  Lesley 
that  as  much  as  35,000  feet  of  rock  have  been  re- 
moved by  denudation.  But  this  being  from  an  anti- 
clinal arch,  it  does  not,  of  course,  afford  any  measure 
of  the  extent  of  the  denudation  of  the  surrounding 
country.  Major  J.  W.  Powell,  Director  of  the  U.S. 
Geol.  Survey,  found  that  under  a  similar  condition  as 
much  as  three  and  a  half  miles  of  strata  have  been 
removed  by  denudation  from  the  top  of  "anticlinal  beds 
in  the  Uinta  Mountains.4 

Probably  the  most  enormous  displacement  of 
strata  which  has  yet  been  found  is  that  of  the 
"  Wahsatch  Fault,"  Utah.  This  fault  is  about  100 


1  Geological  Exploration  of  the  Fortieth  Parallel,  vol.  ii.  p.  456. 

2  Geological  Studies,  p.  92 ;  see  also  Button's  Tertiary  History 
of  the  Canon  District. 

8  Tertiary  History  of  the  Canon  District,  pp.  20,  113;  Second 
Annual  Report,  U.S.  Geol.  Survey,  p.  125. 
4  Powell's  Geology  of  Uinta  Mountains. 


AGE   OF  THE  SUN'S  HEAT  59 

miles  in  length,  crossing  the  fortieth  parallel  of 
latitude  from  north  to  south,  with  a  downthrow  to 
the  west  of  not  less  than  40,000  feet.  So  clear  is  the 
evidence  regarding  this  fault  that  Mr.  Clarence  King 
says  "  that  there  can  be  no  doubt  of  the  quantita- 
tive correctness  of  my  reading  of  this  tremendous 
dislocation."  l 

There  are  other  modes  than  the  foregoing  by 
means  of  which  geologists  are  enabled  to  measure  the 
thickness"*  of  strata  which  may  have  been  removed  in 
places  off  the  present  surface  of  the  country.  Into 
the  details  of  these  I  need  not  here  enter  ;  but  I  may 
give  a  few  examples  of  the  enormous  extent  to  which 
the  country,  in  some  places,  has  been  found  to  have 
been  lowered  by  denudation. 

Dr.  A.  Geikie  has  shown2  that  the  Pentlands  must 
at  one  time  have  been  covered  with  Carboniferous 
rocks,  upwards  of  a  mile  in  thickness,  which  have  all 
been  removed  by  denudation. 

In  the  Bristol  coal-fields,  between  the  river  Avon 
and  the  Mendips,  Sir  Andrew  C.  Eamsay  has  shown3 
that  about  9,000  feet  of  Carboniferous  strata  have  been 
removed  by  denudation  from  the  present  surface. 

Between  Bendrick  Kock  and  Garth  Hill,  South 
Glamorganshire,  a  mass  of  Carboniferous  and  Old 
Red  Sandstone,  of  upwards  of  9,000  feet,  has  been 
removed.  At  the  Vale  of  Towy,  Caermarthenshire, 
about  6,000  feet  of  Silurian  and  5,000  feet  of  Old  Red 


1  Geological  Exploration  of  the  Fortieth  Parallel,  vol.  i.  p.  745. 

8  Memoir  to  Sheet  32,  Geol.  Survey  of  Scotland. 

*  Denudation  of  South  Wales.    Memoirs  of  GeoL  Survey,  vol.  i 


CO  STELLAR  EVOLUTION 

Sandstone — in  all  about  11,000  vertical  feet — have 
been  swept  away.  Between  Llandovery  and  Aber- 
aeron  a  mass  of  about  12,000  vertical  feet  of  the 
Silurian  series  has  been  removed  by  denudation. 
Between  Ebwy  and  the  Forest  of  Dean,  a  distance  of 
upwards  of  20  miles,  a  thickness  of  rock  varying  from 
5,000  to  10,000  feet  has  been  abstracted. 

Prof.  Hull  found1  on  the  northern  flanks  of  the 
Pendle  Eange,  Lancashire,  the  Permian  beds  resting 
on  the  denuded  edges  of  the  Millstone  Grit,  and  these 
were  again  observed  resting  on  the  Upper  Coal- 
measures  south  of  the  Wigan  coal-field.  Now  from 
the  known  thickness  of  the  Carboniferous  series  in 
this  part  of  Lancashire  he  was  enabled  to  calculate 
approximately  the  quantity  of  Carboniferous  strata 
which  must  have  been  carried  away  between  the  period 
of  the  Millstone  Grit  and  the  deposition  of  the  Per- 
mian beds,  and  found  that  it  actually  amounted  to  no 
less  than  9,900  feet.  He  also  found  in  the  Vale  of 
Clitheroe,  and  at  the  base  of  the  Pendle  Eange,  that 
the  Coal-measures,  the  whole  of  the  Millstone  Grit, 
the  Yoredale  series,  and  part  of  the  Carboniferous 
Limestone,  amounting  in  all  to  nearly  20,000  feet, 
had  been  swept  away — an  amount  of  denudation 
which,  as  Prof.  Hull  remarks,  cannot  fail  to  impress 
us  with  some  idea  of  the  prodigious  lapse  of  time 
necessary  for  its  accomplishment. 

It  may  be  observed  that,  enormous  as  is  the 
amount  of  denudation  indicated  by  the*  foregoing 
figures,  these  figures  do  not  represent  in  most  cases 

1  Quart.  Journ.  Oeol.  Soc.  vol.  xxiv.  p.  323. 


AGE   OF  THE  SUN'S  HEAT  61 

the  actual  thickness  of  rock  removed  from  the  surface. 
We  are  necessitated  to  conclude  that  a  mass  of  rock 
equal  to  the  thickness  stated  must  have  been  removed, 
but  we  are  in  moot  cases  left  in  uncertainty  as  to  the 
total  thickness  "which  has  actually  been  carried  away. 
It  cannot  be  imagined  that  these  great  disruptions 
occurred  first  when  the  surface  became  subject  to  de- 
nuding agencies,  or  that  denudation  ceased  to  operate 
precisely  when  the  inequality  was  smoothed  away. 
Moreover,  during  the  time  the  surface  on  one  side  of 
the  fault  was  being  reduced,  some  amount  of  denuda- 
tion must  also  have  been  in  progress  on  the  other  and 
lower  side.  In  the  case  of  a  fault,  for  example,  with  a 
displacement  of,  say,  one  mile,  where  no  indication  of 
it  is  seen  at  the  surface  of  the  ground,  we  know  that 
on  one  side  of  the  fault  a  thickness  of  rock  equal  to  one 
mile  must  have  been  denuded,  but  we  do  not  know 
how  much  more  than  that  may  have  been  removed. 
For  anything  which  we  know  to  the  contrary,  hundreds 
of  feet  of  rock  may  have  been  removed  before  the  dis- 
location took  place,  and  as  many  more  hundreds  after 
all  indications  of  dislocation  had  been  effaced  at  the 
surface. 

But  it  must  be  observed  that  the  total  quantity  of 
rock  which  has  been  removed  from  the  present  surface 
of  the  land  is  evidently  small  in  proportion  to  the  total 
quantity  removed  during  the  past  history  of  our  globe. 
For  those  thousands  and  thousands  of  feet  of  rock 
which  have  been  denuded  were  formed  out  of  the 
waste  of  previously  existing  rocks,  just  as  these  had 
been  formed  out  of  the  waste  of  yet  older  rock-masses. 
7 


62  8TELLAE  EVOLUTION 

In  short,  as  a  general  rule,  the  rocks  of  one  epoch 
have  been  formed  out  of  those  of  preceding  periods, 
and  go  themselves  to  form  those  of  subsequent  epochs. 

In  many  of  the  cases  of  enormous  denudation  to 
which  we  have  referred,  the  erosion  has  been  effected 
during  a  limited  geological  epoch.  We  have,  for 
example,  seen  that  upwards  of  a  mile  in  thickness  of 
Carboniferous  rock  has  been  denuded  in  the  area  of 
the  Pentlands.  But  the  Pentlands  themselves,  it  can 
be  proved,  existed  as  hills,  in  much  their  present  form, 
before  the  Carboniferous  rocks  were  laid  down  over 
them ;  and  as  they  are  of  Lower  Old  Eed  Sandstone 
age,  and  have  been  formed  by  denudation,  they  must 
consequently  have  been  carved  out  of  the  solid  rock 
between  the  period  of  the  Old  Eed  Sandstone  and  the 
beginning  of  the  Carboniferous  age.  This  affords  us 
some  conception  of  the  immense  lapse  of  time  repre- 
sented by  the  Middle  and  Upper  Old  Eed  Sandstone 
periods. 

Again,  in  the  case  of  the  great  fault  separating  the 
Silurians  of  the  south  of  Scotland  from  the  Old  Eed 
Sandstone  tracts  lying  to  the  north,  a  thickness  of 
the  latter  strata  of  probably  more  than  a  mile,  as  we 
have  seen,  must  have  been  removed  from  the  ground 
to  the  south  of  the  fault  before  the  commencement  of 
the  Carboniferous  period.  And  again,  in  the  case  of 
the  Lancashire  coal-fields,  to  which  reference  has  been 
made,  nearly  two  miles  in  thickness  of  strata  had 
been  removed  in  the  interval  which  elapsed  between 
the  Millstone  Grit  and  the  Permian  periods. 

Time  required   to   effect   the  foregoing   amount  of 


AGE  OF  THE  SUN'S  HEAT  63 

denudation. — To  lower  the  country  one  mile  by 
denudation  would  therefore  require,  according  to 
the  rate  which  we  have  already  established,  about 
15,000,000  years  ;  but  we  have  seen  that  a  thickness 
of  rock  more  than  equal  to  that  must  have  been 
swept  away  since  the  Carboniferous  period ;  and  even 
during  the  Carboniferous  period  itself  more  than  a 
mile  in  thickness  of  strata  in  many  places  was 
removed.  Again,  there  can  be  no  doubt  whatever 
that  the  amount  of  rock  removed  during  the  Old  Ked 
Sandstone  period  was  much  greater  than  one  mile  ; 
for  we  know  perfectly  well  that  over  large  tracts 
of  country  nearly  a  mile  in  thickness  of  rock  was 
carried  away  between  the  period  of  the  Lower  Old  Red 
Sandstone  and  the  Carboniferous  epoch.  Further,  all 
geological  facts  go  to  show  that  the  time  represented 
by  the  Lower  Old  Eed  Sandstone  itself  must  have 
been  enormous. 

Now,  three  miles  of  rock  removed  since  the 
commencement  of  the  Old  Eed  Sandstone  period 
(which,  doubtless,  is  an  under-estimate)  would  give  us 
45,000,000  years. 

Again,  going  farther  back,  we  find  the  lapse  of 
time  represented  by  the  Silurian  period  to  be  even 
more  striking  than  that  of  the  Old  Eed  Sandstone. 
The  unconformities  in  the  Silurian  series  indicate 
that  many  thousands  of  feet  of  these  strata  were 
denuded  before  overlying  members  of  the  same  great 
formations  were  deposited.  And  again,  this  immense 
formation  was  formed  in  the  ocean  by  the  slow  de- 
nudation of  pre-existing  Cambrian  continents,  just  aa 


64  STELLAR  EVOLUTION 

these  had  been  huilt  up  out  of  the  ruins  of  the  still 
prior  Laurentian  land.  And  even  here  we  do  not 
reach  the  end  of  the  series,  for  the  Laurentians 
themselves  resulted  from  the  denudation,  not  of  the 
primary  rocks  of  the  globe,  but  of  previously  existing 
sedimentary  and  probably  igneous  rocks,  of  which, 
perhaps,  no  recognisable  portion  now  remains. 

It  is  the  opinion  of  Mr.  Darwin,  and  also  of  Mr. 
Wallace,  that  the  geological  time  which  elapsed  an- 
terior to  the  Cambrian  period  was  as  long  as  the 
whole  interval  from  that  period  to  the  present  day. 
This  is  an  opinion  which  I  suppose  is  supported  by 
most  geologists.  But,  to  err  on  the  safe  side,  I  shall 
assume  that  the  time  which  had  elapsed  prior  to  the 
Old  Eed  Sandstone  was  not  greater  than  the  time 
which  has  elapsed  since  that  period.  Even  on  this 
assumption  we  have  at  least  90,000,000  years  as  a 
minimum  duration  of  geological  time. 

Age  of  the  earth  as  determined  by  the  date  of  the 
glacial  epoch. — Professor  A.  Winchell,  by  a  most 
careful  examination  of  the  probable  relative  lengths 
of  geological  periods,  arrived  at  the  conclusion  that 
the  time  which  elapsed  since  the  beginning  of  the 
glacial  epoch  is  to  the  time  which  has  elapsed  since 
the  solidification  of  the  earth's  surface  as  1  to  250.1 
According  to  the  eccentricity  theory  of  the  cause  of 
the  glacial  epoch,  that  epoch  began  240,000  years 
ago ;  consequently  this  makes  the  time  since  solidifi- 
cation took  place  60,000,000  years,  a  period  which 
agrees  roughly  with  that  deduced  from  denudation, 

1  World  Life,  p.  369. 


AGE  OF  THE  SUN'S  HEAT  65 

and  is  so  far  presumptive  evidence  of  the  truth  of  that 
theory  of  the  cause  of  the  glacial  cold. 

Testimony  of  Biology. — The  time  required  for  the 
variation  and  modification  of  organic  forms  has,  Mr. 
Alfred  E.  Wallace  states,  been  generally  considered  to 
require  an  even  longer  series  of  ages  than  might 
satisfy  the  demands  of  physical  geology.  This  is  a 
point,  however,  on  which  I  am  not  qualified  to  venture 
an  opinion.  I  shall  simply  refer  to  the  views  held  by 
our  highest  authorities  on  the  subject. 

Eeferring  to  Professor  Huxley's  anniversary  ad- 
dress to  the  Geological  Society  in  1870,  where  he 
shows  that  almost  all  the  higher  forms  of  life  must 
have  existed  during  the  Palaeozoic  period,  Mr.  Wallace 
says :  "  Thus,  from  the  fact  that  almost  the  whole  of 
the  Tertiary  period  has  been  required  to  convert  the 
ancestral  Orohippus  into  the  true  horse,  he,  Professor 
Huxley,  believes  that,  in  order  to  have  time  for  the 
much  greater  change  of  the  ancestral  ungulata  into 
the  two  great  odd-toed  and  even-toed  divisions  (of 
which  change  there  is  no  trace  even  among  the  earliest 
Eocene  mammals),  we  should  require  a  large  portion, 
if  not  the  whole,  of  the  Mesozoic  or  Secondary  period. 
Another  case  is  furnished  by  the  bats  and  whales, 
both  of  which  strange  modifications  of  the  mammalian 
type  occur  perfectly  developed  in  the  Eocene  forma- 
tion. What  countless  ages  back  must  we,  then,  go  for 
the  origin  of  these  groups,  the  whales  from  some  an- 
cestral carnivorous  animal,  and  the  bats  from  the 
insectivora  !  And  even  then  we  have  to  seek  for  the 
common  origin  of  carnivora,  insectivora,  ungulata, 


66  STELLAR  EVOLUTION 

and  marsupials  at  a  far  earlier  period ;  so  that,  on  the 
lowest  estimate,  we  must  place  the  origin  of  the  mam- 
malia very  far  back  in  Palaeozoic  times." l 

"  If  the  very  small  differences,"  says  Professor 
Huxley,2 "  which  are  observable  between  the  Crocodilia 
of  the  older  Mesozoic  formations  and  those  of  the  pre- 
sent day  furnish  any  sort  of  approximation  towards 
an  estimate  of  the  average  rate  of  change  among  the 
Sauropsida,  it  is  almost  appalling  to  reflect  how  far 
back  in  Palaeozoic  times  we  must  go  before  we  can 
hope  to  arrive  at  that  common  stock  from  which  the 
Crocodilia,  Lacertilia,  Ornithoscelida,  and  Plesiosauria, 
which  had  attained  so  great  a  development  in  the 
Triassic  epoch,  must  have  been  derived. 

"  The  Amphibia  and  Pisces  tell  the  same  story. 
There  is  not  a  single  class  of  vertebrated  animals 
which,  when  it  first  appears,  is  represented  by  ana- 
logues of  the  lowest  known  members  of  the  same  class. 
Therefore,  if  there  is  any  truth  in  the  doctrine  of 
evolution,  every  class  must  be  vastly  older  than  the 
first  record  of  its  appearance  upon  the  surface  of  the 
globe.  But  if  considerations  of  this  kind  compel  us 
to  place  the  origin  of  vertebrated  animals  at  a  period 
sufficiently  distant  from  the  Upper  Silurian,  in  which 
the  first  Elasmobranchs  and  Ganoids  occur,  to  allow 
of  the  evolution  of  such  fishes  as  these  from  a 
vertebrate  as  simple  as  the  Amphioxus,  I  can  only 
repeat  that  it  is  appalling  to  speculate  upon  the 
extent  to  which  that  origin  must  have  preceded  the 

1  Island  Life,  p.  204. 

2  Quart.  Journ.  of  Geol.  Soc.  vol.  xxvi.  p.  53. 


AGE  OF  THE  SUN'S  HEAT  67 

epoch  of  the  first  recorded  appearance  of  vertebrate 
life." 

"  If  the  theory  be  true,"  says  Mr.  Darwin,  "  it  is  in- 
disputable that  before  the  lowest  Cambrian  stratum 
was  deposited  long  periods  elapsed — as  long  as,  or 
probably  far  longer  than,  the  whole  interval  from  the 
Cambrian  age  to  the  present  day;  and  that  during 
these  vast  periods  the  world  swarmed  with  living 
creatures." l 

In  referring  to  the  abundant  and  well-developed 
fauna  of  the  Cambrian  period,  Sir  Andrew  C.  Eamsay 
remarks  : 2  "In  this  earliest  known  varied  life  we  find 
no  evidence  of  its  having  lived  near  the  beginning  of 
the  Zoological  series.  In  a  broad  sense,  compared 
with  what  must  have  gone  before,  both  biologically 
and  physically,  all  the  phenomena  connected  with  this 
old  period  seem,  to  my  mind,  to  be  quite  of  a  recent 
description ;  and  the  climates  of  seas  and  lands  were 
of  the  very  same  kind  as  those  that  the  world  enjoys 
at  the  present  day — one  proof  of  which,  in  my  opinion, 
is  the  existence  of  great  glacial  boulder  beds  in  the 
Lower  Silurian  strata  of  Wigtonshire,  west  of  Loch 
Kyan." 

Professor  Haeckel  remarks  that  "  Darwin's  theory, 
as  well  as  that  of  Lyell,  renders  the  assumption  of  im- 
mense periods  absolutely  necessary.  If  the  theory  of 
development  be  true  at  all,  there  must  certainly  have 
elapsed  immense  periods,  utterly  inconceivable  to  us." 

In  reference  to  the  foregoing,  Mr.  Wallace  says  : 3 

1  Origin  of  Species,  p.  286. 

8  Proceedings  of  the  Royal  Society,  No.  152,  1874,  p.  342. 

"  Island  Life,  p.  205. 


68  STELLAR  EVOLUTION 

"  These  opinions,  and  the  facts  on  which  they  are 
founded,  are  so  weighty  that  we  can  hardly  doubt 
that,  if  the  time  since  the  Cambrian  epoch  is  correctly 
estimated  at  200,000,000  of  years,1  the  date  of  the 
commencement  of  life  on  the  earth  cannot  be  much 
less  than  500,000,000 ;  while  it  may  not  improbably 
have  been  longer,  because  the  reaction  of  the  organism 
under  changes  of  the  environment  is  believed  to  have 
been  less  active  in  low  and  simple  than  in  high  and 
complex  forms  of  life,  and  thus  the  processes  of  organic 
development  may  for  countless  ages  have  been  exces- 
sively slow." 

I  think  it  must  now  be  perfectly  evident  that  the 
facts  both  of  geology  and  of  biology  are  utterly  irrecon- 
cilable with  the  theory  that  the  sun's  heat  was  derived 
from  the  condensation  of  its  mass  by  gravitation ;  and 
that  the  mistake  in  regard  to  geological  time  has  been 
committed  by  the  physicist,  and  not  by  the  geologist. 
The  grounds  upon  which  the  geologists  and  the 
biologists  found  the  conclusion  that  it  is  more  than 
20  or  30  millions  of  years  since  life  began  on  the 
earth  are  far  more  certain  and  reliable  than  the 
grounds  upon  which  the  physicist  concludes  that  the 
period  must  be  less.  The  only  real  ground  that  the 
physicist  has  is  that  according  to  the  theory  which  he 
holds  of  the  origin  of  the  sun's  heat  a  longer  period  is 
not  possible.  This  might  be  considered  good  evidence 
were  no  other  theory  possible ;  but  there  is  another 
theory,  which  accords  with  all  the  facts,  and  conse- 
quently has  a  strong  presumption  in  its  favour. 

1  Of   course,  Mr.  Wallace  does  not  believe  that  it  is  actually 
200,000,000  years  since  the  Cambrian  period. 


PAET  in. 

EVIDENCE  IN  SUPPOBT  OF  THE  THEOEY  FROM 
THE  FEE-NEBULAR  CONDITION  OF  THE  UNI- 
VERSE. 

THE  nebular  hypothesis,  strictly  speaking,  is  one 
simply  intended  to  account  for  the  origin  of  our  solar 
system.  "It  is,"  as  remarks  Professor  A.  Winchell, 
"  primarily  a  genetic  explanation  of  the  phenomena  of 
the  solar  system ;  and  accessorily  a  co-ordination,  in  a 
common  conception,  of  the  principal  phenomena  in 
the  stellar  and  nebular  firmament,  as  far  as  human 
vision  has  been  able  to  penetrate."  l  The  theory  starts 
with  the  assumption  that  all  the  materials  composing 
the  solar  system  once  existed  in  a  state  of  extreme 
tenuity  and  diffusion,  filling  far  more  than  the  entire 
space  included  within  the  orbit  of  the  most  remote 
planet.  It  begins  with  this  diffused  nebulous  mass 
tending  slowly,  under  the  influence  of  gravitation, 
towards  a  state  of  aggregation.  Beyond  this  point 
the  received  nebular  hypothesis  does  not  extend. 

It  will  be  observed  that  the  theory  here  begins  in 
the  middle  of  a  process.  It  begins  with  the  assump- 
tion of  a  mass  in  the  act  of  condensing  under  the 
influence  of  gravity.  It  offers  no  explanation  of 
the  origin  of  the  mass,  or  how  it  came  to  be  in  this 

1  World  Life,  p.  19F, 


70  STELLAE  EVOLUTION 

attenuated  state,  or  in  what  condition  it  existed  before 
the  materials  began  to  draw  together.  These  are, 
however,  inquiries  which  naturally  force  themselves 
on  our  attention.  If  the  nebular  theory  be  a  true 
theory  of  the  origin  of  the  solar  system,  then 
this  nebulous  mass  must  have  had  an  antecedent 
history,  and  we  cannot  help  feeling  the  instinctive 
desire  of  tracing  the  chain  of  causation  farther  back. 
The  mind  presses  towards  an  absolute  beginning. 
It  is  the  goal  to  which  it  aspires,  and  no  amount  of 
failure  will  ever  deter  it  from  renewing  its  efforts. 
Of  recent  years  a  considerable  amount  of  attention 
has  been  devoted  to  inquiries  in  this  direction ;  nearly 
all  of  which,  it  is  true,  has  necessarily  been  of  a  specu- 
lative and  hypothetical  character.  But  hypothesis, 
as  Mr.  Locyker  remarks,  is  the  life-blood  of  investiga- 
tion. 

The  nebular  hypothesis  is  so  highly  probable  as  to 
have  gained  almost  universal  acceptance.  In  fact,  it 
contains  very  little  of  a  hypothetical  nature.  It  is,  as 
Mr.  Mill  says,  "  an  example  of  legitimate  reasoning 
from  a  present  effect  to  its  past  cause,  according  tq 
the  known  laws  of  that  cause."  Like  the  hypothesis 
of  a  luminiferous  ether,  if  it  is  not  a  true  theory,  one 
would  almost  think  that  it  deserves  to  be  so. 

There  seems  no  reason  why  inquiries  should  stop 
at  the  point  where  Laplace  began.  The  same  line  of 
reasoning  may  yet  carry  us  back  into  the  pre-nebular 
region,  and  perhaps  with  as  great  a  degree  of  certainty 
as  it  has  done  in  the  nebular ;  though,  no  doubt,  the 
farther  back  we  proceed,  the  more  difficult  probably 


PBE-NEBULAR  CONDITION  OF  THE  UNIVEESE  71 

will  the  inquiry  become.  But,  be  all  this  as  it  may, 
there  can  be  little  doubt  that  the  path  of  investigation 
is  a  legitimate  one,  and  also  one  which  is  worthy  of 
being  traced  out. 

I  shall  now  briefly  refer  to  some  of  the  leading 
views  which  have  been  expressed  in  regard  to  the 
pre-nebular  history  of  the  universe,  and  shall  after- 
wards consider  the  additional  light  which  the  theory 
discussed  in  this  volume  seems  to  cast  on  the 
subject. 

The  commonly  received  opinion  is  that  the  nebulaa 
were  formed  from  ordinary  matter  existing  in  a  high 
state  of  division,  and  widely  diffused  through  space. 
The  "  cosmical  dust,"  as  it  is  called,  was  the  universal 
"  world-stuff,"  out  of  which  all  things  were  supposed 
to  be  formed.  It  is  held  that  in  receding  backwards 
in  pre-nebular  times,  the  smaller,  more  simple,  and 
elementary  the  materials  were.  Out  of  this  primi- 
tive cosmical  dust,  or  world-stuff,  by  aggregation,  the 
materials  became  successively  larger  and  more  com- 
plex. The  theory  of  the  origin  of  nebulae,  on  this 
principle,  has  been  clearly  stated  by  Professor  "Win- 
chell,  and  I  here  give  a  brief  outline  of  his  views  on 
the  subject. 

.  Professor  A.  Winchell  on  the  pre-nebular  condition  of 
matter. — This  cosmical  dust,  or  world-stuff,  he  con- 
siders to  be  scattered  promiscuously  through  bound- 
less space.  It  is  cold  and  non-luminous,  and  is  acted 
upon  by  forces  of  attraction  and  probably  of  repulsion. 
The  material  particles,  either  as  atoms  or  less  pro- 
bably as  molecules,  are  drawn  by  mutual  attraction 


72  STELLAR  EVOLUTION 

into  groups  and  swarms.  Any  central  attractive 
force,  as  of  a  sun  or  planet,  by  causing  the  parti- 
cles to  move  in  converging  lines,  would  cause  them 
to  become  approximated  and  ultimately  aggregated. 
Thus  both  mutual  attractions  and  centric  movements 
would  tend  to  produce  aggregations  dispersed  through 
space.  But  in  the  presence  of  two  or  more  attractive 
centres,  as  in  the  present  constitution  of  the  Cosmos, 
it  is  impossible  that  any  mass  shall  fall  directly  upon 
its  centre  of  attraction.  Hence  motions  of  rotation 
will  be  established  in  the  mass,  and  also  orbital  mo- 
tions of  masses  about  each  other.  In  addition  to  the 
mutual  attraction  of  the  molecules,  the  convergence 
of  their  paths  towards  centres  of  attraction  must  also 
tend  to  the  formation  of  masses  and  swarms  of  masses 
and  particles.  "  We  have  then,"  he  says,  "  to  picture 
indefinite  space  as  pervaded  by  swarms  of  masses  and 
particles  of  dark  matter.  Each  mass  or  particle  may, 
nevertheless,  be  separated  by  thousands  of  miles.  It 
is  manifest,  therefore,  that  each  mass  or  particle  will 
eventually  dispose  itself,  under  the  fixed  action  of  the 
forces  of  matter,  in  some  definite  order.  '  It  is  mani- 
fest also,  from  what  has  been  said,  that  each  swarm 
will  have  a  progressive  motion  along  a  path  having 
the  essential  character  of  an  orbit  around  some  domi- 
nant centre  of  attraction.  If,  as  seems  to  be  the  fact, 
an  ethereal  medium,  or  any  condition  of  interplane- 
tary matter,  exists  in  space,  it  opposes  the  movements 
of  these  swarms  by  opposing  the  motion  of  each  con- 
stituent mass.  But  the  smaller  masses — the  parti- 
cles and  molecules — would  feel  this  resistance  to  the 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  73 

greatest  extent.  They  would  therefore  fall  behind  the 
heavier  masses,  and  would  be  most  deflected  toward 
the  attracting  centre.  The  smallest  particles  would 
be  driven  farthest  to  the  rear,  and  dispersed  farthest 
from  the  orbit  of  the  train,  along  the  side  turned 
toward  the  principal  attraction.  The  swarm  would 
present  an  elongated  form,  in  which  the  larger  and 
heavier  masses  would  move  foremost,  and  nearest  the 
line  of  the  orbit — that  is,  near  the  exterior  skirt  of 
the  area  covered  by  the  general  swarm — while  the 
smaller  ones  would  follow,  in  graduated  succession, 
in  a  long  train  which  would  present  a  fan-like  expan- 
sion lying  mostly  on  the  inside  of  the  path  of  the 
principal  masses." 

"  This,  it  may  be  conceived,  is  the  mode  of  aggre- 
gation of  these  cosmical  matters  in  the  depths  of 
space.  Of  course  the  attractions  which  control  them 
are  feeble  ;  their  movements  are  slow,  the  resistances 
are  relatively  inconsiderable,  and  the  elongation  of 
the  swarm  is  correspondingly  inconspicuous.  What  I 
have  described  is  a  tendency  which  would  be  present. 
Sometimes  the  controlling  attraction  would  be  only 
another  cosmical  swarm.  The  two  swarms  would  re- 
volve similarly  about  their  common  centre  of  gravity, 
while  prolonged  resistances  would  cause  their  slow 
approximation  and  final  coalescence  at  the  common 
centre  of  gravity.  Sometimes  the  controlling  attrac- 
tion would  be  exerted  by  a  distant  sun,  around  which 
it  would  slowly  move,  continually  gathering  up  addi- 
tions of  matter  from  the  wide  fields  of  space." 

"  In  most  cases  all  controlling  attraction  would  be 
8 


74  STELLAR  EVOLUTION 

feebly  felt.  These  clouds  of  cosmical  dust  would  float 
practically  poised  in  the  raidst  of  space,  and  would 
gradually  grow  by  the  continued  accession  of  new 
matter.  Some  of  them  would  become  aggregates  of 
large  dimensions,  and  their  attraction  would  be  dis- 
tinctly felt  by  other  aggregates.  There  would  be  a 
tendency  of  such  aggregates  to  approach  each  other. 
They  might  possibly  approach  along  a  straight  line ; 
but  more  probably  some  third  aggregation,  or  some 
distant  sun,  would  deflect  them  into  orbits  about  their 
common  centre  of  gravity,  in  which,  by  prolonged 
collisions  of  cosmical  matter,  they  are  brought  to 
ultimate  coalescence  with  each  other.  Or  some  other 
attractive  disturbance  affords  such  a  resultant  of 
actions  as  may  bring  them  more  directly  together. 
When  these  larger  aggregations  of  world-stuff  come 
together,  the  result  is  an  aggregation  approaching 
the  dimensions  of  the  Herschellian  nebulae."  l 

In  regard  to  the  origin  of  the  heat  of  the  nebulae, 
I  am  glad  to"  find  that  Professor  Winchell,  to  a  certain 
extent,  adopts  the  views  which  I  have  so  long  enter- 
tained on  the  subject.  "  The  thought,"  he  says,  "  must 
already  have  suggested  itself  to  the  reader  that  the 
process  of  conglomeration  affords  an  explanation  of 
the  intense  heat  which  vaporises  its  substance,  and 
causes  it  to  yield  a  spectrum  of  bright  lines.  As  the 
sudden  compression  of  a  portion  of  atmospheric  air 
yields  heat  sufficient  to  ignite  tinder,  or  fuse  and 
volatilise  a  descending  meteor-mass,  so  the  precipita- 
tion of  one  planet  upon  another  would  liberate  suffi- 

1  World  Life,  p.  72. 


PEE -NEBULAE  CONDITION  OF  THE  UNIVERSE  75 

cient  heat  to  reduce  them  both  to  a  state  of  fusion,  or 
even  of  vapour.  Still  more  must  the  intensest  heat 
be  generated  by  the  impact  of  two  nebulous  masses, 
one  or  both  of  which  together  may  embrace  more 
matter  than  all  our  planets  and  the  sun  combined — 
as  much  even  as  the  matter  of  our  entire  visible  fir- 
mament of  stars.  One  experiences  a  distinct  feeling 
of  relief  in  the  discovery  of  such  a  possible  means  of 
ignition  of  nebulae." 

Mr.  Charles  Morris  on  the  pre-nebular  condition 
of  matter. — Others  again  suppose  matter  to  be  present 
everywhere  throughout  space.  This  view  has  been 
ingeniously  advocated  by  Mr.  Charles  Morris  in  an 
article  on  "  The  Matter  of  Space,"  which  appeared  in 
Nature,  February  8,  1883.  The  hypothesis  of  an 
ether  specially  distinct  from  matter  he  considers  to 
be  a  gratuitous  assumption,  and  one  of  the  last  sur- 
viving relics  of  eighteenth  century  science,  and,  unless 
it  can  be  proved  that  highly  disintegrated  matter  is 
positively  incapable  of  conveying  light  vibrations, 
there  is  no  warrant  for  assigning  this  duty  to  a  dis- 
tinct form  of  substance.  But  that  matter  exists  in 
outer  space  in  the  same  conditions  as  in  planetary 
atmospheres  he  thinks  is  improbable.  Its  duty  as  a 
conveyer  of  radiant  vibrations  seems  to  require  a  far 
greater  tensity,  and  its  disintegration  is  probably  ex- 
treme. Assuming  matter  throughout  the  universe — 
here  as  condensed  spheres,  and  there  in  outer  space 
as  highly  rarified  substance — the  atmospheric  enve- 
lopes of  the  spheres,  he  considers,  will  gradually  shade 
off  into  the  excessively  rare  matter  of  mid-space. 


76  STELLAE  EVOLUTION 

Matter  may  exist  in  countless  conditions  as  to  sim- 
plicity and  complexity,  &c.,  but  the  base  particle  he 
assumes  to  be  the  same  under  all  conditions.  In  the 
spheres  there  is  matter  ranging  from  the  simplest 
elementary  gases,  through  the  mineral  compounds  of 
the  solid  surface,  to  the  highly  compounded  organic 
molecules.  In  outer  space  the  variation  is  in  the 
opposite  direction ;  the  matter  existing  there  in  a 
highly  disintegrated  condition. 

Every  particle  he  considers  to  possess  a  certain 
amount  of  motor  energy  in  the  form  of  heat.  As  the 
total  amount  of  this  energy  in  the  universe  remains 
unchanged,  a  particle  can  only  lose  energy  by  trans- 
ferring it  to  others.  This  heat  energy  acts,  of  course, 
in  opposition  to  gravity :  it  tends  to  repel  the  par- 
ticles from  each  other,  while  gravity,  on  the  other 
hand,  tends  to  draw  them  together.  The  former  acts 
as  a  centrifugal,  the  latter  as  a  centripetal  energy. 
If  the  heat  momentum  of  the  particles  be  insufficient 
to  constitute  a  centrifugal  energy  equal  to  the  centri- 
petal energy  of  gravitation,  then  the  material  contents 
of  space  will  be  drawn  into  the  attracting  spheres  as 
atmospheric  substance,  and  outer  space,  in  this  case, 
will  be  left  destitute  of  matter.  If,  on  the  contrary, 
the  centrifugal  energy  of  the  particles  be  sufficient  to 
resist  gravitation,  then  the  particles  will  remain  free, 
and  space  will  continue  to  be  occupied  with  matter. 
As  has  been  stated,  the  sum  of  motor  energy  in 
the  universe  remaining  unchanged,  the  aggrega- 
tion of  atmospheric  substance  around  any  planet 
resulting  from  the  loss  of  motor  energy  must 


PEE -NEBULAE  CONDITION  OF  THE  UNIVEESE  77 

cause  an  increase  of  motor  energy  in  the  particles 
outside. 

The  theory  seems  to  dispense  with  the  necessity 
for  assuming  a  luminiferous  ether,  for  the  functions 
attributed  to  the  ether  may,  it  is  thought,  be  per- 
formed by  the  particles  themselves ;  a  view  which  has 
been  advocated  by  Euler,  Grove,  and  others.  The 
origin  of  nebulae,  according  to  the  theory,  is  accounted 
for  as  follows  : 

"  The  nebular  hypothesis,"  says  Mr.  Morris,  "  holds 
that  the  matter  now  concentrated  into  suns  and 
planets  was  once  more  widely  disseminated,  so  that 
the  substance  of  each  sphere  occupied  a  very  con- 
siderable extent  of  space.  It  even  declares  that  the 
matter  of  the  solar  system  was  a  nebulous  cloud, 
extending  far  beyond  the  present  limits  of  that  system. 
From  this  original  condition  the  existing  condition  of 
the  spheres  has  arisen  through  a  continued  concen- 
tration of  matter.  But  this  concentration  was  con- 
stantly opposed  by  the  heat  energy  of  the  particles, 
or,  in  other  words,  by  their  centrifugal  momentum. 
This  momentum  could  only  be  got  rid  of  by  a  redis- 
tribution of  motor  energy.  If,  for  illustration,  the 
average  momentum  of  the  particles  of  the  nebulae  was 
just  equivalent  to  their  gravitative  energy,  then  a 
portion  of  this  energy  must  radiate  or  be  conducted 
outwards  ere  the  internal  particles  could  be  held 
prisoners  by  gravitation.  The  loss  of  momentum 
inwardly  must  be  correlated  with  an  increase  of 
momentum  outwardly. 

"  This  is  a  necessary   consequence  of  the  heat 


78  STELLAR  EVOLUTION 

relations  of  matter.  As  substance  condenses,  its  capa- 
city for  heat  decreases  and  its  temperature  rises, 
hence  a  difference  of  temperature  must  constantly 
have  arisen  between  the  denser  and  the  rarer  portions 
of  the  nebulous  mass,  and  equality  of  temperature 
could  be  restored  only  by  heat  radiation.  This  radia- 
tion still  continues,  and  must  continue  until  con- 
densation ceases  and  the  temperatures  of  the  spheres 
and  space  become  equalised ;  but  this  is  equivalent  to 
declaring  that  as  the  particles  of  the  spheres  decrease 
in  heat  momentum  those  of  interspheral  space  in- 
crease, and  if  originally  the  centrifugal  and  centri- 
petal energies  of  matter  approached  equality  they 
must  become  unequal,  centripetal  energy  becoming 
in  excess  in  spheral  matter,  centrifugal  energy  in  the 
matter  of  space.  Thus,  as  a  portion  of  the  widely 
distributed  nebulous  matter  lost  its  heat,  and  became 
permanently  fixed  in  place  by  gravitative  attraction, 
another  portion  gained  heat,  became  still  more  inde- 
pendent of  gravity,  and  assumed  a  state  of  greater 
nebulous  diffusion  than  originally.  The  condensing 
spheres  only  denuded  space  of  a  portion  of  the  matter 
which  it  formerly  held,  and  left  the  remainder  more 
thinly  distributed  than  before.  The  spheres,  in  their 
concentration,  have  emitted,  and  are  emitting,  a  vast 
energy  of  motion.  This  motor  energy  yet  exists  in 
space  as  a  motion  of  the  particles  of  matter,  which, 
therefore,  press  upon  each  other,  or  seek  to  extend 
their  limits,  with  increasing  vigour,  so  that  the  elas- 
ticity of  interspheral  matter  is  constantly  increasing." 
Sir  William  E.  Grove  on  the  pre-nebular  con- 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  79 

dition  of  matter. — Amongst  the  first  to  advocate  the 
view  that  ordinary  matter  is  everywhere  present  in 
space  was  Sir  William  E.  Grove.  In  a  lecture 
delivered  at  the  London  Institution  as  far  back  as 
January  1842,  he  stated  that  it  appeared  to  him 
that  heat  and  light,  according  to  the  undulatory 
theory,  were  the  result  of  the  vibrations  of  ordinary 
matter  itself,  and  not  that  of  a  distinct  ethereal  fluid. 
Twenty  years  afterwards,  referring  to  the  views  he 
then  advanced,  he  says :  "  Although  this  theory  has 
been  considered  defective  by  a  philosopher  of  high 
repute,  I  cannot  see  the  force  of  the  arguments  by 
which  it  has  been  assailed ;  and,  therefore,  for  the 
present,  though  with  diffidence,  I  still  adhere  to  it."  l 

He  adduces  a  great  many  facts  and  forcible  argu- 
ments in  support  of  his  position.  He  says  that 
"  there  appears  no  reason  why  the  atmosphere  of  the 
different  planets  should  not  be,  with  reference  to  each 
other,  in  a  state  of  equilibrium.  Ether,  or  the  highly 
attenuated  matter  existing  in  the  interplanetary 
space,  being  an  expansion  of  some  or  all  of  these 
atmospheres,  or  of  the  more  volatile  portions  of  them, 
would  thus  furnish  matter  for  the  transmission  of 
the  modes  of  motion  which  we  call  light,  heat,  &c." 
It  is  assumed  in  the  theory,  of  course,  that  matter 
must  form  a  universal  planum. 

Sir  William  Grove  favours  the  idea  that  the  uni- 
verse is  illimitable  in  extent,  a  view  held  by  many 
eminent  thinkers. 

1  Correlation  of  Physical  Forces,  p.  164  (fifth  edition),  1867. 


80  STELLAE  EVOLUTION 


EVOLUTION  OF  THE  CHEMICAL  ELEMENTS,  AND  ITS 
EELATIONS  TO  STELLAR  EVOLUTION. 

We  come  now  to  the  consideration  of  a  subject 
which  has  a  most  important  bearing  on  the  question 
of  stellar  evolution,  viz.  the  genesis  and  dissociation 
of  the  chemical  elements.  The  evolution  of  one 
element  from  another  is,  it  is  true,  as  yet  but  a  mere 
hypothesis,  but  it  is  an  hypothesis  well  supported  by 
a  host  of  facts  and  considerations,  and  held  by  a  large 
number  of  our  leading  chemists  and  physicists.  "  The 
demonstrated  unity  of  force,"  says  Professor  F.  W. 
Clarke,1  "leads  us  by  analogy  to  expect  a  similar  unity 
of  matter ;  and  the  many  strange  and  hitherto  un- 
explained relations  between  the  different  elements 
tend  to  encourage  our  expectations."  The  hypothesis 
throws  much  light  on  some  obscure  points  in  stellar 
evolution.  In  regard  to  this,  Professor  Clarke  justly 
remarks  that  "  it  is  plain  that  the  nebular  hypothesis 
would  be  doubled  in  importance,  and  our  views  of  the 
universe  greatly  expanded,  if  it  could  be  shown  that 
an  evolution  of  complex  from  simple  forms  of  matter 
accompanied  the  development  of  planets  from  the 
nebulae.  Evolution  could  look  for  no  grander  triumph." 
In  fact,  it  is  difficult  to  understand  how  our  sun  and 
the  stars  could  have  been  evolved  from  nebulae  without 
assuming  an  evolution  of  the  chemical  elements.  The 
true  nebulae  show  the  presence  of  only  two  elements, 
nitrogen  and  hydrogen,  but  our  sun  contains  more 

1  Popular  Science  Monthly  for  January  1873. 


PEE-NEBULAE  CONDITION  OF  THE  UNIVEESE  81 

than  a  dozen  of  distinct  elements,  and  the  planets 
more  than  three  times  that  number.  How,  then,  could 
all  these  have  arisen  out  of  nebulae  composed  simply 
of  nitrogen  and  hydrogen  ?  The  matter  is  plain  if  we 
assume  an  evolution  of  the  elements. 

The  stars  have  been  classed  into  four  groups, 
which,  as  Professor  Clarke  has  remarked,  indicate 
different  stages  in  the  process  of  evolution.  The  first 
class,  containing  white  stars  like  Sirius,  show  the  pre- 
dominance of  hydrogen  and  a  scarcity  of  the  metallic 
elements.  In  the  second  class  the  metallic  elements 
become  more  numerous  and  the  hydrogen  less  dis- 
tinct; while- in  the  third  class  hydrogen  is  difficult  to 
detect.1  This  seems  to  show  a  gradual  development 
.of  the  chemical  elements  as  the  star  cools  and  grows 
older.  I  shall  now  give  a  brief  account  of  the  views 
expressed  on  the  subject  by  some  of  our  leading 
physicists  and  chemists. 

It  will  be  observed,  in  reference  to  the  theories  we 
have  just  considered,  that  the  process  of  evolution  is 
supposed  to  take  place  from  the  smaller  to  the  larger 
aggregates  of  matter.  Beginning  with  an  extreme 
condition  of  tenuity,  by  aggregation,  the  materials 
become  successively  larger  and  more  complex.  In 
passing  backwards  in  the  process  we  find  the  aggre- 
gates becoming  less  and  less  till  they  reach  the 
"  cosmical  dust,"  or  "  fire-mist,"  out  of  which  the 
primitive  nebulae  were  supposed  to  be  formed.  Ee- 
ceding  still  farther  back,  we  have  the  universal 

1  See  also  on  this  point  Mr.  Lockyer's  "  Bakerian  Lecture,"  Proc. 
Boy.  Soc.  No.  266,  p.  21. 


82  STELLAR  EVOLUTION 

atmosphere  from  which  the  fire-mist  is  assumed  to 
have  been  derived. 

This  universal  atmosphere,  though  in  a  state  of 
extreme  tenuity,  is,  as  we  shall  see,  supposed  by  some 
to  be  in  a  more  elemental  form  than  anything  revealed 
to  us  in  the  laboratory.  The  suggestion  of  the  dis- 
sociation of  the  chemical  elements  and  its  application 
to  stellar  physics  was,  I  think,  first  advanced  by  Sir 
Benjamin  Brodie  in  1866,  and  more  fully  in  1867.  In 
the  latter  year  views  similar  were  considered  more 
fully  by  Dr.  T.  Sterry  Hunt.  The  question  of  the 
dissociation  of  elements  has  been  ably  discussed  by 
Mr.  Lockyer  in  his  various  writings.  It  has  been 
suggested  by  Mr.  Lockyer  that  the  coincidence  of  rays 
emitted  by  different  chemical  elements  when  subjected 
to  very  high  temperatures  affords  evidence  of  a  com- 
mon element  in  the  composition  of  the  metals  pro- 
ducing the  coincident  rays.  Mr.  Lockyer  states  that 
many  trains  of  thought  suggested  by  solar  and  stellar 
physics  point  to  the  hypothesis  that  the  elements 
themselves,  or  at  all  events  some  of  them,  are  compound 
bodies.1  This  view  was  also  put  forward  by  Professor 
Graham,  who  says  "that  it  is  conceivable  that  the 
various  kinds  of  matter  now  recognised  in  different 
elementary  substances  may  possess  one  and  the  same 
element  or  atomic  molecule  existing  in  different  con- 
ditions of  mobility.  The  essential  unity  of  matter," 
he  adds,  "  is  an  hypothesis  in  harmony  with  the 
equal  action  of  gravity  upon  all  bodies."  Similar 
views  have  been  advocated  by  M.  Dumas,  who  based 

1  Proc.  Boy.  Soc.  vol.  xxviii.  p.  160. 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  83 

the  suggestion  of  the  composite  nature  of  the  ele- 
mentary atoms  on  certain  relations  of  atomic  weights. 
The  composite  nature  of  the  chemical  elements  has 
also  been  maintained  by  Henri  Sainte-Claire  Deville, 
and  also  by  Berthelot,  who  held  that  the  atoms  of  the 
elements  are  the  same,  and  distinguished  only  by 
their  modes  of  motion.  Professor  Schuster,  in  a 
paper  read  before  the  British  Association  in  1880, 
supports  the  view  of  the  dissociation  of  the  chemical 
elements. 

That  all  the  purely  physical  sciences  will  one  day 
be  brought  under  a  few  general  laws  and  principles, 
and  the  whole  of  the  recognised  chemical  elements 
will  be  resolved  into  one  or  two  material  elements,  is 
a  conclusion  towards  which  physical  science  seems  at 
present  slowly  tending.  There  is  certainly  something 
fascinating  in  this  view  of  the  unity  of  nature. 
There  is  in  this  idea  more  than  a  purely  physical 
interest  attached  to  it.  It  has,  as  I  hope  to  show 
in  a  future  work,  an  important  bearing  on  questions 
relating  to  the  foundations  of  the  true  theory  of 
evolution. 

The  question  of  the  unity  of  the  chemical  elements 
is  one,  however,  yet  in  a  hypothetical  condition.  Pro- 
fessors Liveing  and  Dewar,  who  have  given  attention 
to  this  subject,  say :  "The  supposition  that  the  different 
elements  may  be  resolved  into  simpler  constituents,  or 
into  a  single  one,  has  long  been  a  favourite  specula- 
tion with  chemists ;  but,  however  probable  this  hypo- 
thesis may  appear  a  priori,  it  must  be  acknowledged 
that  the  facts  derived  from  the  most  powerful  method 


84  STELLAE  EVOLUTION 

of  analytical  investigation  yet  devised  give  it  scant 
support."  l 

Sir  Benjamin  Brodie  on  the  pre-nebular  condition  of 
matter. — There  are,  considers  Sir  Benjamin  Brodie, 
very  forcible  reasons  which  lead  us  to  suspect  that 
chemical  substances  are  really  composed  of  a  primi- 
tive system  of  elemental  bodies,  analogous  in  their 
general  nature  to  our  present  elements :  that  some  of 
those  bodies  which  we  speak  of  as  elements  may  be 
compounds.  These  ideal  elements  assumed  by  him, 
he  says,  "  though  now  revealed  to  us  by  the  numerical 
properties  of  chemical  equations  only  as  implicit  and 
dependent  existences,  we  cannot  but  surmise  may  some- 
times become,  or  may  in  the  past  have  been,  isolated 
and  independent  existences  " — as,  for  instance,  in  the 
case  of  the  sun,  where  the  temperature  is  excessive. 
"  We  may,"  he  further  adds,  "  consider  that  in  remote 
ages  the  temperature  of  matter  was  much  higher  than 
it  is  now,  and  that  these  other  things  [ideal  elements] 
existed  then  in  the  state  of  perfect  gases — separate 
existences — uncombined."  2  He  then  refers  to  certain 
observations  of  Mr.  Huggins  and  Dr.  Miller  on  the 
spectra  of  nebulas  where  one  of  the  lines  of  nitrogen, 
was  found  alone ;  and  that  this  suggested  to  them  that 
the  line  might  have  been  produced  by  one  of  the 
elements  of  nitrogen ;  and  that  nitrogen  may  there- 
fore be  compound.  He  mentions  as  a  significant  fact 
that  a  large  proportion  of  the  class  of  elements  which 
he  has  termed  "  composite  elements  "  has  not  been 


Proc.  Roy.  Soc.  vol.  xxxii.  p.  230. 
Ideal  Chemistry,  p.  56. 


PEE-NEBULAE  CONDITION  OF  THE  UNIVERSE  85 

found  in  the  sun,  they  having  probably  been  decom- 
posed by  the  intense  heat. 

Dr.  T.  Sterry  Hunt  on  the  pre-nebular  condition  of 
matter. — A  year  after  the  foregoing  views  regarding 
chemical  dissociation  had  been  advanced  by  Sir 
Benjamin  Brodie,  Dr.  T.  Sterry  Hunt,  in  a  lecture  on 
"  The  Chemistry  of  the  Primeval  Earth,"  delivered  at 
the  Eoyal  Institution  (May  31,  1867),  put  forward, 
apparently  quite  independently,  opinions  on  dissocia- 
tion similar  to  those  of  Brodie.  In  this  lecture  he 
says  :  "  I  considered  the  chemistry  of  nebulae,  sun,  and 
stars  in  the  combined  light  of  spectroscopic  analysis 
and  Deville's  researches  on  dissociation,  and  con- 
cluded with  the  generalisation  that  the  breaking-up 
of  compounds,  or  dissociation  of  elements,  by  intense 
heat  is  a  principle  of  universal  application,  so  that 
we  may  suppose  that  all  the  elements  which  make 
up  the  sun,  or  our  planet,  would,  when  so  intensely 
heated  as  to  be  in  the  gaseous  condition  which  all 
matter  is  capable  of  assuming,  remain  uncombined, 
that  is  to  say,  would  exist  together  in  the  state 
of  chemical  elements,  whose  further  dissociation  in 
stellar  or  nebulous  masses  may  even  give  us  evidence 
of  matter  still  more  elemental  than  that  revealed  ifi 
the  experiments  of  the  laboratory,  where  we  can  only 
conjecture  the  compound  nature  of  many  of  the  so- 
called  elementary  substances."  l  And  in  hie  address 
at  the  grave  of  Priestley  he  referred  to  the  suggestion 
of  Lavoisier  that  hydrogen,  nitrogen,  and  oxygen, 
with  heat  and  light,  might  be  regarded  as  simpler 

1  American  Journal  of  Science,  vol.  xxiii.  p.  124. 
9 


86  STELLAR  EVOLUTION 

forms  of  matter  from  which  all  others  are  derived. 
This  suggestion  was  considered  in  connection  with 
the  fact  that  the  nebulae,  which  we  conceive  to  be 
condensing  into  suns  and  planets,  have  hitherto 
shown  evidences  only  of  the  presence  of  the  first 
two  of  these  elements,  which,  as  is  well  known, 
make  up  a  large  part  of  the  gaseous  envelope  of  our 
planet,  in  the  forms  of  air  and  aqueous  vapour. 
With  this  he  connected  the  hypothesis  advanced  by 
Grove,  "  that  our  atmosphere  and  ocean  are  but 
portions  of  the  universal  medium  which,  in  an  at- 
tenuated form,  fills  the  interstellary  spaces  ; l  and 
further  suggested  as  a  legitimate  and  plausible 
speculation  that  these  same  nebulae  and  their  re- 
sulting worlds  may  be  evolved  by  a  process  oj 
chemical  condensation  from  this  universal  atmosphere^ 
to  which  they  would  sustain  a  relation  somewhat 


1 "  Our  atmosphere,"  says  Dr.  Hunt,"  is  not  terrestrial,  but  cosmical, 
being  a  universal  medium  diffused  throughout  all  space,  but  condensed 
around  the  various  centres  of  attraction  in  amount  proportional  to 
their  mass  and  temperature,  the  waters  of  the  ocean  themselves 
belonging  to  this  universal  atmosphere."  (Nature,  August  29,  1878, 
p.  475.)  Similar  views  have  been  advocated  by  Mr.  Mattieu  Williams, 
who  says  "  that  the  gaseous  ocean,  in  which  we  are  immersed,  is  but 
a  portion  of  the  infinite  atmosphere  that  fills  the  whole  solidity  of 
space;  that  links  together  all  the  elements  of  the  universe,  and 
diffuses  among  them  their  heat  and  light,  and  all  the  other  physical 
and  vital  forces  which  heat  and  light  are  capable  of  generating." 
(Fuel  of  the  Sun,  p.  5.)  In  1854  Sir  William  Thomson  suggested  the 
idea  that  the  luminiferous  ether  was  probably  a  continuation  of  our 
atmosphere,  though  I  do  not  think  he  continues  to  hold  that  opinion, 
The  first  to  advance  this  idea  was,  undoubtedly,  Newton,  who 
assumed  interplanetary  space  to  be  universally  filled  with  an  ethereal 
medium  "  much  of  the  same  constitution  as  air,  but  far  rarer,  subtler, 
and  more  elastic." 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  87 

analogous  to  that  of  clouds  and  rain  to  the  aqueous 
vapour  around  us." 

Professor  Oliver  Lodge  on  the  pre-nebular  condition 
of  matter. — Some  have  gone  still  farther  back  and 
supposed  that  the  material  universe  may  have  arisen 
out  of  the  luminiferous  ether — the  hypothetical  me- 
dium which  is  assumed  to  pervade  all  space.  The 
universal  world-stuff  scattered  through  boundless 
space  may  in  an  extreme  state  of  attenuation  be, 
says  Professor  Winchell,  the  ethereal  medium,  and 
out  of  this  semi- spiritual  substance  may  have  germi- 
nated the  molecules  of  common  matter.  "  It  is  cer- 
tainly possible,"  he  says,  "  to  conceive  these  cosmical 
atoms  as  a  rising-out  of  some  transformation  of  the 
ethereal  medium ;  but  we  know  too  little  of  the  nature 
of  ether  to  ground  a  scientific  inference  of  this  kind."  * 

The  ethereal  origin  of  matter  has  been  advocated 
by  M.  Saigey,  Dr.  Macvicar,  and  others.  In  a  lecture 
by  Professor  Oliver  Lodge,  delivered  at  the  London 
Institution  in  December  1882,  he  also  advocates 
the  ethereal  origin  of  matter.  "  As  far  as  we  know," 
to  state  his  views  in  his  own  words,  "  this  ether 
appears  to  be  a  perfectly  homogeneous,  incompres- 
sible, continuous  body,  incapable  of  being  resolved 
into  simple  elements  or  atoms  ;  it  is,  in  fact,  con- 
tinuous, not  molecular.  There  is  no  other  body  of 
which  we  can  say  this,  and  hence  the  properties  of 
ether  must  be  somewhat  different  from  those  of 
ordinary  matter."  .  .  .  "  One  naturally  asks,  is  there 
any  such  clear  distinction  to  be  drawn  between  ether 

1  World  Life,  p.  533. 


88  STELLAR  EVOLUTION 

and  matter  as  we  have  hitherto  tacitly  assumed  ? 
May  they  not  be  different  modifications,  or  even 
manifestations,  of  the  same  thing  ?  "  He  then  adopts 
Sir  William  Thomson's  theory  of  vortex  atoms,  into 
the  details  of  which  I  need  not  here  enter.  In  con- 
clusion, says  Professor  Lodge,  "  I  have  now  endea- 
voured to  introduce  you  to  the  simplest  conception  of 
the  material  universe  which  has  yet  occurred  to  man — 
the  conception  that  it  is  of  one  universal  substance, 
perfectly  homogeneous  and  continuous,  and  simple  in 
structure,  extending  to  the  farthest  limits  of  space  of 
which  we  have  any  knowledge,  existing  equally  every- 
where :  some  portions  either  at  rest  or  in  simple  irro- 
tational  motion,  transmitting  the  undulations  which 
we  call  light ;  other  portions  in  rotational  motion — in 
vortices,  that  is — and  differentiated  permanently  from 
the  rest  of  the  medium  by  reason  of  this  motion. 

"  These  whirling  portions  constitute  what  we  call 
matter  ;  their  motion  gives  them  rigidity,  and  of  them 
our  bodies  and  all  other  material  bodies  with  which 
we  are  acquainted  are  built  up. 

"  One  continuous  substance  filling  all  space,  which 
can  vibrate  as  light ;  which  can  be  sheared  into  posi- 
tive and  negative  electricity  ;  which  in  whirls  consti- 
tutes matter ;  and  which  transmits  by  continuity,  and 
not  by  impact,  every  action  and  reaction  of  which 
matter  is  capable.  This  is  the  modern  view  of  ether 
and  its  functions."  1 

There  is  this  objection  to  Professor  Lodge's  theory: 
it  is  purely  hypothetical.  The  vortex  atoms  are  not 

1  Nature,  February  1,  1883,  p.  330. 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  89 

only  hypothetical,  but  the  substance  out  of  which  these 
atoms  are  assumed  to  be  formed  is  also  itself  hypo- 
thetical. We  have  no  certain  evidence  that  such  a 
medium  as  is  thus  supposed  exists,  or  that  a  medium 
possessing  the  qualities  attributed  to  it  could  exist. 
In  fact,  we  have  here  one  hypothesis  built  upon 
another. 

The  vortex  theory  appears  to  me  to  be  beset  by  a 
difficulty  of  another  kind,  viz.  that  of  reconciling  it 
with  the  First  Law  of  Motion.  According  to  that  law  no 
body  possessing  inertia  can  deviate  from  the  straight 
line  unless  forced  to  do  so.  A  planet  will  not  move 
round  the  sun  unless  it  be  constantly  acted  upon  by  a 
force  deflecting  it  from  the  straight  path.  A  grind- 
stone will  not  rotate  on  its  axis  unless  its  particles 
are  held  together  by  a  force  preventing  them  from 
flying  off  at  a  tangent  to  the  curve  in  which  they  are 
moving.  Centrifugal  force  must  always  be  balanced 
by  centripetal  force.  The  difficulty  is  to  understand 
what  force  counterbalances  the  centrifugal  force  of 
the  rotating  material  of  the  vortex-atom.  It  is  not 
because  the  centrifugal  tendency  of  the  rotating 
material  is  controlled  by  the  exterior  incompressible 
fluid,  for  it  offers  no  resistance  whatever  to  the 
passage  of  the  atom  through  it  —  in  short,  in  so 
far  as  the  motion  of  the  atom  is  concerned,  this 
fluid  is  a  perfect  void.  Now,  if  this  fluid  can  offer  no 
resistance  to  the  passage  of  the  atom  as  a  whole,  how 
then  does  it  manage  to  offer  such  enormous  resistance 
to  the  materials  composing  the  atom,  so  as  to  con- 
tinually deflect  them  from  the  straight  path  and 


90  STELLAR  EVOLUTION 

compel  them  to  move  in  a  curve  ?  The  centrifugal 
force  of  these  vortex-atoms  must  be  enormous,  for  on 
it  is  assumed  to  depend  the  hardness  or  resistance  of 
matter  to  pressure.  Now  the  centripetal  force  which 
balances  this  centrifugal  force  must  be  equally  enor- 
mous. If,  then,  this  perfect  fluid  outside  the  vortex- 
atom  can  exert  this  enormous  force  on  the  revolving 
material  without  being  itself  possessed  of  vortex- 
motion,  there  does  not  seem  to  be  any  necessity 
for  vortex-motion  in  order  to  produce  resistance.  In 
short,  how  is  the  existence  of  the  atom  possible  under 
the  physical  conditions  assumed  in  the  theory  ? 
How  this  may  be,  like  the  space  of  four  dimensions, 
may  be  expressed  in  mathematical  language,  but 
like  it,  I  fear,  it  is  unthinkable  as  a  physical  con- 
ception. 

Mr.  William  Crookes  on  the  pre-nebular  condition  of 
matter. — In  his  opening  address  before  the  Chemical 
Section  of  the  British  Association  in  1886,  Mr.  William 
Crookes  entered  at  considerable  length  into  the  ques- 
tion of  the  genesis  and  evolution  of  the  chemical 
elements.  I  shall  here  give  a  brief  statement  of  his 
views  as  embodied  in  his  important  address,  and  this 
I  shall  endeavour  to  do  as  nearly  as  possible  in  Mr. 
Crookes's  own  words. 

"We  ask,"  says  Mr.  Crookes,  "whether  the  chemical 
elements  may  not  have  been  evolved  from  a  few  ante- 
cedent forms  of  matter — or  possibly  from  only  one 
such — just  as  it  is  now  held  that  all  the  innumerable 
variations  of  plants  and  animals  have  been  developed 
from  fewer  and  earlier  forms  of  organic  life :  built  up, 


FEE-NEBULAE  CONDITION  OF  THE  UNIVEESE  91 

as  Dr.  Gladstone  remarks,  from  one  another  according 
to  some  general  plan.  This  building  up,  or  evolution, 
is  above  all  things  not  fortuitous :  the  variation  and 
development  which  we  recognise  in  the  universe  run 
along  certain  fixed  lines  which  have  been  preconceived 
and  foreordained.  To  the  careless  and  hasty  eye 
design  and  evolution  seem  antagonistic ;  the  more 
careful  inquirer  sees  that  evolution,  steadily  proceeding 
along  an  ascending  scale  of  excellence,  is  the  strongest 
argument  in  favour  of  a  preconceived  plan." 

Now,  as  in  the  organic  world,  so  in  the  inorganic, 
it  seems  natural  to  view  the  chemical  elements  not  as 
primordial,  but  as  the  gradual  outcome  of  a  process 
of  development,  possibly  even  of  a  struggle  for  exist- 
ence. But  this  evolution  of  the  elements  must  have 
taken  place  at  a  period  so  remote  as  to  be  difficult  to 
grasp  by  the  imagination,  when  our  earth,  or  rather 
the  matter  of  which  it  consists,  was  in  a  state  very 
different  from  its  present  condition.  The  epoch  of 
elemental  development,  remarks  Mr.  Crookes,  is  de- 
cidedly over,  and  it  may  be  observed  that  in  the 
opinion  of  not  a  few  biologists  the  epoch  of  organic 
development  is  verging  upon  its  close. 

Is  there  then,  in  the  first  place,  any  direct  evidence 
of  the  transmutation  of  any  supposed  "  element  "  of 
our  existing  list  into  another,  or  of  its  resolution  into 
anything  simpler  ?  To  this  question  Mr.  Crookes 
answers  in  the  negative. 

We  find  ourselves  thus  driven  to  indirect  evidence 
— to  that  which  we  may  glean  from  the  mutual  rela- 
tions of  the  elementary  bodies.  First,  we  may  consider 


82  STELLAR  EVOLUTION 

the  conclusion  arrived  at  by  Herschel,  and  pursued  by 
Clerk-Maxwell,  that  atoms  bear  the  impress  of  manu- 
factured articles.  "  A  manufactured  article  may  well 
be  supposed  to  involve  a  manufacturer.  But  it  does 
something  more  :  it  implies  certainly  a  raw  material, 
and  probably,  though  not  certainly,  the  existence  of  by- 
products, residues,  paraleipomena.  What  or  where  is 
here  the  raw  material  ?  Can  we  detect  any  form  of 
matter  which  bears  to  the  chemical  elements  a  relation 
like  that  of  a  raw  material  to  the  finished  product,  like 
that,  say,  of  coal-tar  to  alizarin  ?  Or  can  we  recognise 
any  elementary  bodies  which  seem  like  waste  or  refuse"? 
Or  are  all  the  elements,  according  to  the  common 
view,  co-equals  ?  To  these  questions  no  direct  answers 
are  forthcoming.*' 

Argument  from  Front's  Law.—  The  bearing  of  the 
hypothesis  of  Prout  in  relation  to  the  evolution  of  the 
elements  is  first  considered  by  Mr.  Crookes.  If  that 
hypothesis  were  demonstrated  it  would  show  that  the 
accepted  elements  are  not  co-equal,  but  have  been 
formed  by  a  process  of  expansion  or  evolution.  Ac- 
cording to  this  hypothesis  the  atomic  weights  of  the 
elements  are  multiples  by  a  series  of  whole  numbers 
of  the  atomic  weight  of  hydrogen.  It  is  true  that 
accurate  determinations  of  the  atomic  weights  of  dif- 
ferent elements  do  not  by  any  means  harmonise  with  the 
values  which  Pr out's  Law  requires  ;  nevertheless  the 
agreement  in  so  many  cases  is  so  close  that  one  can 
scarcely  regard  the  coincidence  as  accidental. 

The  atomic  weights  have  been  recalculated  with 
extreme  care  by  Professor  F.  W.  Clarke,  of  Cincin- 


PEE-NEBVLAE  CONDITION  OF  THE  UNIVERSE  93 

nati,  and  he  says  that "  none  of  the  seeming  exceptions 
are  inexplicable.  In  short,  admitting  half-multiples 
as  legitimate,  it  is  more  probable  that  the  few  appa- 
rent exceptions  are  due  to  undetected  constant  errors 
than  that  the  great  number  of  close  agreements  should 
be  merely  accidental."  In  reference  to  this  suggestion 
of  Professor  Clarke,  Mr.  Crookes  thinks  that  it  places 
the  matter  upon  an  entirely  new  basis.  For,  suppose 
the  unit  atom  to  be  not  hydrogen,  but  some  element 
of  still  lower  atomic  weight,  say  helium,  an  element 
supposed  by  many  authorities  to  exist  in  the  sun 
and  other  stellar  bodies — an  element  whose  spectrum 
consists  of  a  single  ray,  and  whose  vapour  possesses 
no  absorbent  power,  which  indicates  a  remarkable 
simplicity  of  molecular  constitution.  Granting  that 
helium  exists,  all  analogy  points,  says  Mr.  Crookes,  to 
its  atomic  weight  being  below  that  of  hydrogen  ;  and 
here,  then,  we  have  the  very  element  with  atomic 
weight  half  that  of  hydrogen  required  by  Professor 
Clarke  as  the  basis  of  Prout's  Law. 

Argument  from  the  earth's  crust. — The  probable 
compound  nature  of  the  chemical  elements,  Mr. 
Crookes  thinks,  is  better  shown  by  a  consideration  of 
certain  peculiarities  in  their  occurrence  in  the  earth's 
crust.  "  We  do  not,"  he  says,  "  find  them  evenly  dis- 
tributed throughout  the  globe.  Nor  are  they  asso- 
ciated in  accordance  with  their  specific  gravities : 
the  lighter  elements  placed  on  or  near  the  surface, 
and  the  heavier  ones  following  serially  deeper  and 
deeper.  Neither  can  we  trace  any  distinct  relation 
between  local  climate  and  mineral  distribution.  And 


04  STELLAR  EVOLUTION 

by  no  means  can  we  say  that  elements  are  always  or 
chiefly  associated  in  nature  in  the  order  of  their  so- 
called  chemical  affinities  :  those  which  have  a  strong 
tendency  to  form  with  each  other  definite  chemical 
combinations  being  found  together,  whilst  those  which 
have  little  or  no  such  tendency  exist  apart.  We  cer- 
tainly find  calcium  as  carbonate  and  sulphate,  sodium 
as  chloride,  silver  and  lead  as  sulphides ;  but  why  do 
we  find  certain  groups  of  elements,  with  little  affinity 
for  each  other,  yet  existing  in  juxtaposition  or  com- 
mixture ?  " 

As  instances  of  such  grouping  he  mentions  nickel 
and  cobalt ;  the  two  groups  of  platinum  metals  ;  and 
the  so-called  "rare  earths,"  existing  in  gadolinite, 
samarskite,  &c.  Why,  then,  are  these  elements  so 
closely  associated  ?  What  agency  has  brought  them 
together  ?  It  cannot  be  considered  that  nickel  and 
cobalt  have  been  deposited  in  admixture  by  organic 
agency  ;  nor  yet  the  groups  of  iridium,  osmium,  and 
platinum ;  ruthenium,  rhodium,  and  palladium. 

These  features,  Mr.  Crookes  thinks,  seem  to  point 
to  their  formation  severally  from  some  common 
material  placed  in  conditions  in  each  case  nearly 
identical. 

Argument  from  the  compound  radicals. — A  strong 
argument  in  favour  of  the  compound  nature  of  the 
elements,  Mr.  Crookes  thinks,  is  derived  from  a  con- 
sideration of  their  analogy  to  the  compound  radicals, 
or  pseudo-elements  as  they  might  be  called.  It  may 
be  fairly  held  that  if  a  body  known  to  be  compound 
is  found  behaving  as  an  element,  this  fact  lends 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  95 

plausibility  to  the  supposition  that  the  elements 
are  not  absolutely  simple.  From  a  comparison  of 
the  physical  properties  of  inorganic  with  those  of 
organic  compounds,  Dr.  Carnelley  concluded  that  the 
elements,  as  a  whole,  are  analogous  to  the  hydro- 
carbon radicals.  This  conclusion,  if  true,  he  added, 
should  lead  to  the  further  inference  that  the  so-called 
elements  are  not  truly  elementary,  but  are  made  up 
of  at  least  two  absolute  elements,  which  he  named 
provisionally  A  and  B. 

In  Dr.  Carnelley's  scheme  all  the  chemical  elements 
save  hydrogen  are  supposed  to  be  composed  of  two 
simpler  elements,  A  =  12  and  B=2.  Of  these  he  re- 
gards A  as  a  tetrad  identical  with  carbon,  and  B  as  a 
monad  of  negative  weight ;  perhaps  the  ethereal  fluid 
of  space.  His  three  primary  elements  are,  therefore, 
carbon,  hydrogen,  and  the  ether. 

Argument  from  polymerisation. — The  polymeristic 
theory  of  the  genesis  of  the  chemical  elements  pro- 
pounded by  Dr.  Mills  falls  next  to  be  considered. 

It  has  been  suggested  by  Dr.  E.  J.  Mills  that  the 
pristine  matter  was  once  in  an  intensely  heated  con- 
dition, and  that  it  has  reached  its  present  state  by  a 
process  of  free  cooling,  and  that  the  elements,  as  we 
now  have  them,  are  the  result  of  successive  polymeri- 
sations. Chemical  substances  in  cooling  naturally 
increase  in  density,  and  we  sometimes  observe  that  as 
the  density  increases  there  are  critical  points  corre- 
sponding to  the  formation  of  new  and  well- denned 
substances.  The  bodies  thus  formed  are  known  as 
polymers.  From  a  study  of  the  classification  of  the 


96  STELLAE  EVOLUTION 

elements  Mr.  Mills  is  of  opinion  that  the  only  known 
polymers  of  the  primitive  matter  are  arsenic,  anti- 
mony, and  perhaps  erbium  and  osmium. 

Argument  from  the  Periodic  Law.— Lastly  a  scheme 
of  the  origin  of  the  elements,  suggested  to  Mr.  Crookes 
by  consideration  of  Professor  Keynolds's  method  of 
illustrating  the  periodic  law  of  Newlands,  is  discussed. 

It  was  pointed  out  by  Newlands  that  atomicity 
and  other  properties  of  some  of  the  chemical  elements 
depend  on  the  order  in  which  their  atomic  weights 
succeeded  one  another ;  and  when  this  law  was  ex- 
tended by  Professor  Mendelejeff  to  all  elements  it  was 
apparent  that  a  mathematical  relation  exists  between 
the  elements.  This  far-reaching  law  has  been  fruitful 
of  results.  Keferring  to  Professor  Keynolds's  diagram 
illustrating  the  law,  Mr.  Crookes  says  :  "  The  more  I 
study  the  arrangement  of  this  zigzag  curve,  the  more 
I  am  convinced  that  he  who  grasps  the  key  will  be 
permitted  to  unlock  some  of  the  deepest  mysteries  of 
creation.  Let  us  imagine  if  it  is  possible  to  get  a 
glimpse  of  a  few  of  the  secrets  here  hidden.  Let  us 
picture  tl^e  very  beginnings  of  time,  before  geological 
ages,  before  the  earth  was  thrown  off  from  the  central 
nucleus  of  molten  fluid,  before  even  the  sun  himself 
had  consolidated  from  the  original  protyle.1  Let  us 
still  imagine  that  at  this  primal  stage  all  was  in  an 
ultra-gaseous  state,  at  a  temperature  inconceivably 

1  Protyle  is  the  term  adopted  by  Mr.  Crookes  to  designate  the 
original  primal  matter  existing  before  the  evolution  of  the  chemical 
elements,  and  out  of  which  they  v/ere  evolved.  Protyle  in  chemistry 
is  analogous  to  protoplasm  in  biology,  with  this  difference,  however, 
that  protyle  is  as  yet  hypothetical,  whereas  protoplasm  is  known  to 
be  real. 


PEE-NEBULAE  CONDITION  OF  THE  UNIVEESE  97 

hotter  than  anything  now  existing  in  the  visible  uni- 
verse ;  so  high,  indeed,  that  the  chemical  atoms  could 
not  yet  have  been  formed,  being  still  far  above  their 
dissociation-point.  In  so  far  as  protyle  is  capable  of 
radiating  or  reflecting  light,  this  vast  sea  of  incan- 
descent mist,  to  an  astronomer  in  a  distant  star, 
might  have  appeared  as  a  nebula,  showing  in  the 
spectroscope  a  few  isolated  lines,  forecasts  of  hydro- 
gen, carbon,  and  nitrogen  spectra. 

"  But  in  course  of  time  some  process  akin  to  cool- 
ing, probably  internal,  reduces  the  temperature  of  the 
cosmic  protyle  to  a  point  at  which  the  first  step  in 
granulation  takes  place ;  matter  as  we  know  it  comes 
into  existence,  and  atoms  are  formed.  As  soon  as  an 
atom  is  formed  out  of  protyle  it  is  a  store  of  energy, 
potential  (from  its  tendency  to  coalesce  with  other 
atoms  by  gravitation  or  chemically)  and  kinetic  (from 
its  internal  motions).  To  obtain  this  energy,  the 
neighbouring  protyle  must  be  refrigerated  by  it,  and 
thereby  the  subsequent  formation  of  other  atoms  will 
be  accelerated.  But  with  atomic  matter  the  various 
forms  of  energy  which  require  matter  to  render  them 
evident  begin  to  act ;  and,  amongst  others,  that  form 
of  energy  which  has  for  one  of  its  factors  what  we 
now  call  atomic  weight.  Let  us  assume  that  the 
elementary  protyle  contains  within  itself  the  poten- 
tiality of  every  possible  combining  proportion  or 
atomic  weight.  Let  it  be  granted  that  the  whole  of 
our  known  elements  were  not  .at  this  epoch  simulta- 
neously created.  The  easiest  formed  element,  the 

one  most  nearly  allied  to  the  protyle  in  simplicity,  ia 
10 


98  STELLAR  EVOLUTION 

first  born.  Hydrogen — or  shall  we  say  helium  ? — of  all 
the  known  elements  the  one  of  simplest  structure  and 
lowest  atomic  weight,  is  the  first  to  come  into  being. 
For  some  time  hydrogen  would  be  the  only  form  of 
matter  (as  we  know  it)  in  existence,  and  between 
hydrogen  and  the  next  formed  element  there  would  be 
a  considerable  gap  in  time,  during  the  latter  part  of 
which  the  element  next  in  order  of  simplicity  would 
be  slowly  approaching  its  birth-point :  pending  this 
period  we  may  suppose  that  the  evolutionary  process, 
which  soon  was  to  determine  the  birth  of  a  new 
element,  would  also  determine  its  atomic  weight,  its 
affinities,  and  its  chemical  position." 

Professor  F.  W.  Clarke  on  the  pre-nebular  condi- 
tion of  matter. — Views  on  elemental  evolution  almost 
similar  to  those  of  Mr.  Crookes's  have  been  advocated 
by  Professor  Clarke.  Spectroscopic  phenomena,  says 
Professor  Clarke,  are  quite  in  harmony  with  the  idea 
that  all  matter  is  at  bottom  one,  our  supposed  atoms 
being  really  various  aggregations  of  the  same  funda- 
mental unit. 

"  Everybody  knows  that  the  nebular  hypothesis,  as 
it  is  to-day,  draws  its  strongest  support  from  spectro- 
scopic  facts.  There  shine  the  nebulae  in  the  heavens, 
and  the  spectroscope  tells  us  what  they  really  are, 
namely,  vast  clouds  of  incandescent  gas,  mainly,  if  not 
entirely,  hydrogen  and  nitrogen.  If  we  attempt  to 
trace  the  chain  of  evolution  through  which  our  planet 
is  supposed  to  have  grown,  we  shall  find  the  sky  is 
full  of  intermediate  forms.  The  nebulae  themselves 
appear  to  be  in  various  stages  of  development ;  the 


PEE -NEBULAR  CONDITION  OF  THE  UNIVERSE  99 

fixed  stars  or  suns  differ  widely  in  chemical  consti- 
tution, and  in  temperature ;  our  earth  is  most  com- 
plex of  all.  There  are  no  '  missing  links  '  such  as 
the  zoologist  longs  to  discover  when  he  tries  to  ex- 
plain the  origin  of  species.  First,  we  have  a  nebula 
containing  little  more  than  hydrogen,  then  a  very  hot 
star  with  calcium,  magnesium,  and  one  or  two  other 
metals  added ;  next  comes  a  cooler  sun  in  which  free 
hydrogen  is  missing,  but  whose  chemical  complexity 
is  much  increased ;  at  last  we  reach  the  true  planets 
with  their  multitudes  of  material  forms.  Could  there 
well  be  a  more  straightforward  story  ?  Could  the 
unity  of  creation  receive  a  much  more  ringing  em- 
phasis? We  see  the  evolution  of  planets  from 
nebulae  still  going  on,  and  parallel  with  it  an  evolu- 
tion of  higher  from  lower  kinds  of  matter. 

"  Just  here,  perhaps,  is  the  key  to  the  whole  sub- 
ject. If  the  elements  are  all  in  essence  one,  how 
could  their  many  forms  originate  save  by  a  process 
of  evolution  upward  ?  How  could  their  numerous 
relations  with  each  other,  and  their  regular  serial  ar- 
rangements into  groups,  be  better  explained  ?  In  this, 
as  in  other  problems,  the  hypothesis  of  evolution  is 
the  simplest,  most  natural,  and  best  iri  accordance 
with  facts." » 

Dr.  G.  Johnstone  Stoney  on  the  pre-nehdar  condi- 
tion of  matter. — Further  evidence  that  all  the  chemi- 
cal elements  were  probably  evolved  from  one  common 
source,  is  furnished  by  Dr.  G.  Johnstone  Stoney 5s 

1  Popular  Scietice  Monthly  for  February  1876.    See  also  the 
January  number  for  1873. 


100  STELLAR  EVOLUTION 

"Logarithmic  Law  of  Atomic  Weights,"  a  theory 
recently  advanced  in  a  communication  to  the  Eoyal 
Society.1  A  cardinal  feature  of  this  investigation  is 
that  in  it  atomic  weights  are  represented  by  volumes, 
not  by  lines.  A  succession  of  spheres  are  taken  whose 
volumes  are  proportional  to  the  atomic  weights,  and 
which  may  be  called  the  atomic  spheres.  When  the 
radii  of  these  spheres  are  plotted  down  on  a  diagram 
as  ordinates,  and  a  series  of  integers  as  abscissas,  the 
general  form  of  the  logarithmic  curve  becomes  appa- 
rent; and  close  scrutiny  has  shown  that  either  the 
logarithmic  curve,  or  some  curve  lying  very  close  to 
it,  expresses  the  real  law  of  nature. 

If,  as  seems  probable,  the  logarithmic  law  is  the 
law  of  nature,  there  appear  to  be  three  elements 
lighter  than  hydrogen,  which  Dr.  Stoney  has  termed 
infra-fluorine,  infra-oxygen,  and  infra-nitrogen.  And 
there  are,  at  all  events,  six  missing  elements  between 
hydrogen  and  lithium. 

Dr.  Stoney's  investigation  is  based  on  the  fact  that 
if  the  atomic  weights  of  the  chemical  elements  be 
arranged  in  order  of  magnitude,  periodic  laws  come 
to  light,  viz. :  those  discovered  by  Newlands,  Mende- 
lejeff,  and  Meyer.  From  this  it  follows  that  there 
must  be  some  law  connecting  the  atomic  weights  with 
the  successive  terms  of  a  numerical  series — either 
alone  or  along  with  other  variables. 

"  This  law,"  says  Dr.  Stoney,  "  may  be  obtained  in 
one  of  its  graphical  forms  by  plotting  down  a  series 
of  integers  as  abscissas,  and  the  successive  atomic 

1  Proc.  Roy.  Soc.  for  April  19,  1888.  p.  115. 


PBE-NEBULAR  CONDITION  OF  THE  UNIVERSE  101 

weights  as  ordinates.  In  this  way  it  furnishes  a  dia- 
gram which  has  somewhat  the  shape  of  a  hurling- 
stick,  consisting  of  a  short  curved  portion  succeeded  by 
a  long  and  nearly  straight  portion.  But  as  this  diagram 
cannot  be  directly  identified  with  any  known  curve, 
it  does  not  suffice  for  the  determination  of  the  law. 

"  The  diagram,  however,  assumes  a  form  which  can 
be  interpreted  when  we  use  the  cube  roots  of  the 
atomic  weights  for  its  ordinates,  instead  of  the  atomic 
weights  themselves.  This  is  equivalent  to  taking 
volumes  instead  of  lines  to  represent  the  atomic 
weights.  When  this  is  done,  the  ends  of  the  ordinates 
are  found  to  lie  near  a  regular  and  gradual  curve, 
from  which  they  deviate  to  the  right  and  left  by  dis- 
placements that  are  small  and  appear  to  follow  periodic 
laws  which  have  been  in  part  traced.  The  central 
curve  is  found  on  examination  to  be  either  a  logarith- 
mic curve  or  some  curve  lying  exceedingly  close  to  it. 
If  the  curve  be  in  reality  the  logarithmic  curve,  it 
furnishes  us  the  law  that : 

"  The  cube  root  of  the  nth  atomic  weight —K  log  (n  q) 
4-  a  small  periodic  correction ;  where  K  and  q  are 
constants,  the  values  of  which  are  furnished  by  the 
observations. 

"  Either  this  logarithmic  law,  or  a  law  that  lies  ex- 
ceedingly close  to  it,  must  be  the  law  of  nature." 

Referring  to  this  theory,  Professor  Keynolds  says  : 
"  It  certainly  introduced  points  of  extraordinary  im- 
portance, though  perhaps  at  present  they  could  not  all 
quite  realise  its  fullest  import.  There  were  several 
points  of  some  little  difficulty  to  be  grappled  with,  but 


102  STELLAR  EVOLUTION 

it  clearly  pointed  to  the  conclusion  that  we  were  fast 
approaching  the  time  when  physicists — both  chemical 
and  physicists  proper — are  combining  to  evolve  out  of 
the  scientific  work  lying  on  the  borderland  most  im- 
portant and  startling  facts." 

The  bearing  which  Dr.  Stoney's  conclusions,  like 
those  of  Mr.  Crookes,  have  on  the  primitive  condition 
of  the  material  universe  is  obvious. 

Dr.  Stoney,  like  Mr.  Crookes,  considers  that  the 
chemical  elements  are  subject  to  decay.  That  they 
are  not  only  generated  but  destroyed — that  they  are 
subject  not  only  to  evolution  but  dissolution.  He 
believes  that  the  generative  process  probably  takes 
place  only  at,  or  beyond,  the  confines  of  the  universe, 
and  the  destructive  process  at  the  centres  of  overgrown 
stars,  which  is  the  position  of  lowest  potential.  Dr. 
Stoney  thinks  that  this  extinction  of  the  chemical 
elements  in  the  centre  of  a  star  is  a  cause  which 
limits  its  size  and  prevents  its  overgrowth. 

THE  IMPACT  THEORY  IN  RELATION  TO  THE  FOREGOING 
THEORIES  OF  THE  PRE-NEBULAR  CONDITION  OP 
MATTER. 

In  all  these  theories,  as  has  already  been  observed, 
the  primitive  condition  of  the  universe  was  that 
of  matter  in  a  state  of  extreme  tenuity,  while  by 
aggregation  the  materials  became  successively  larger 
and  larger  until  they  assumed  the  magnitude  of  suns 
and  planets.  For  example,  according  to  the  meteoric 
theory,  meteorites  are  formed  out  of  "  cosmical  dust," 
"  fire-mist,"  or  condensed  vapour,  and  then  suns 


FEE-NEBULAR  CONDITION  OF  THE  UNIVERSE  103 

and  planets  are  formed  by  aggregation  from  these 
meteorites.  Facts  seem,  however,  to  point  to  the 
very  reverse  as  being  the  true  course  of  events. 

Meteorites  are  undoubtedly  the  fragments  of 
larger  masses.  It  looks  more  likely  that  they  are, 
as  has  already  been  stated,  fragments  of  stellar 
masses  which  have  been  shattered  to  pieces  by 
collision,  and  that  this  "  cosmical  dust,"  from  which 
the  meteorites  are  alleged  to  have  been  formed,  are 
simply  the  dust  arising  out  of  the  destruction  of  the 
masses.  After  the  two  bodies  had  collided  and  been 
shattered  to  pieces,  some  of  the  fragments  would  un- 
doubtedly be  projected  with  a  velocity  that  would 
carry  them  beyond  the  attractive  power  of  the  general 
mass,  and  thus  they  would  escape  being  volatilised. 
These  fragments  would  continue  their  wanderings 
through  space  as  meteorites. 

I  cannot  but  think  that  the  number,  as  well  as 
the  importance,  of  these  wanderers  has  been  greatly 
over-estimated.  Mr.  Lockyer  states  that  Dr.  Schmidt, 
of  Athens,  found  that  the  mean  hourly  number  of 
luminous  meteors  visible  on  a  clear  moonless  night 
by  one  observer  was  fourteen.  Certainly  no  such 
quantity  is  visible  in  this  country.  In  Scotland,  at 
least,  one  may  often  watch  night  after  night  under 
the  most  favourable  conditions  without  having  the 
good  fortune  to  see  a  single  meteor. 

It  is,  of  course,  true  that  the  immediately  prior 
condition  of  a  sun  or  a  planet  was  that  of  matter  in 
an  extremely  attenuated  or  dissociated  state.  This 
is  essential  to  the  nebular,  as  well  as  to  the  meteoric, 


104  STELLAR  EVOLUTION 

hypothesis.     But  it  is  not  with  the  immediately  prior 
condition  that  we  are  at  present  concerned,  but  with 
the  primitive,  or  pre-nebular,  condition.     Take,  for 
example,  the  case  of  the  solar  nebula,  out  of  which 
our  sun  and  planets  were  formed.     Was  this  nebu- 
lous mass  formed  from  matter  in  a  state  of  extreme 
tenuity,  scattered  through   space  and   collected  to- 
gether by  gravity  ?     Or  did  it  result  from  two  solid 
globes  shattered  to   pieces  by   collision,  which  were 
then   converted   into  the  nebulous  condition  by  the 
heat  generated  from  the  collision  ?    It  is  no  doubt 
true  that  the  analogies  of  nature  would,  at  first  sight, 
be  apt  to  lead  us  to  the  conclusion  that  the  former 
theory  was  the  more  likely  of  the  two,  as  the  larger 
is  generally  made  by  aggregation  from  the  smaller. 
But   a   little   consideration   will   show  that,   in   the 
present   case,   the  weight  of  this  analogy  is  more 
apparent  than  real.     The  impact  theory  does  not  rest 
upon  a  purely  hypothetical  basis.   The  cause  to  which 
it  appeals  has  a  real  existence.     The  point  of  un- 
certainty is  whether  the  cause  actually  produces  the 
effect  which  is   attributed  to  it.      We   know   from 
observation  that  there  are  stellar   masses,  some  of 
them  probably  larger  than  our  sun,  moving  through 
space   with   enormous   velocities    in   all    directions.1 
According  to  the  ordinary  laws  of  chance,  collision  at 
times  would  be  an  inevitable  result,  and  when  such 
an  event  did  take  place  the  destruction  of  the  colliding 
bodies,  and  their  consequent   transformation  into  a 

1  The  dark  stellar  masses  which  escape  observation  may  be  as 
numerous  as  those  that  are  visible. 


PRE-NEBULAB  CONDITION  OF  THE  UNIVERSE  105 

nebulous  mass,  would,  at  least  in  many  cases,  be  a 
necessary  result.  In  fact,  we  have,  in  the  case  of 
these  vast  stellar  masses,  what  we  know  occurs  among 
the  invisible  molecules  of  a  gas.  So  far  as  mere  . 
analogy  is  concerned,  the  impact  theory  is  just  about 
as  probable  as  the  other. 

From  what  has  been  stated  it  would  follow  that  in 
most  cases  the  stellar  masses  have  been  formed  out 
of  the  destruction  of  pre-existing  masses,  like  the 
geological  formations  out  of  the  destruction  of  prior 
formations. 

The  theories  do  not  account  for  the  motion  of  the 
stars. — According  to  all  the  foregoing  theories  aggre- 
gation and  condensation  are  produced  by  gravity. 
The  materials  dispersed  throughout  space  are  drawn 
together  by  their  mutual  attraction,  and  aggregated 
round  a  centre  of  gravity.  Gravitation,  although  it 
imparts  motion  to  the  materials,  can  impart  no  motion 
of  translation  to  the  mass  itself.  Gravitation  cannot, 
therefore,  be  the  cause  of  the  motion  of  translation  of 
the  mass.  The  stars  are  not  supposed  to  be  gravi- 
tating towards,  or  around,  a  great  centre  of  attraction, 
for  they  are  found  moving  in  straight  lines  in  all 
directions,  which  could  not  be  the  case  if  gravity  were 
the  cause  of  their  motion.  To  what  cause  is  their 
motion,  therefore,  to  be  attributed  ?  A  meteorite  or 
other  small  body  might  be  ejected  from  any  system, 
by  the  explosive  force  of  heat  or  some  other  cause, 
with  a  velocity  which  might  carry  it  into  boundless 
space  ;  but  such  could  not  be  the  case  in  regard  to  a 
body  of  the  magnitude  of  a  star.  No  one  for  a  moment 


106  STELLAR  EVOLUTION 

could  suppose  that  1830  Groombridge,  for  example, 
moving  at  the  rate  of  200  miles  a  second,  is  an  eject 
from  any  system. 

According  to  the  impact  theory  the  whole  is  plain ; 
for  this  200  miles  per  second  is  simply  a  part  of  the 
untransformed  motion  of  translation  which  the  mate- 
rials composing  the  star  had  from  the  beginning.  In 
other  words,  the  matter  and  the  motion  were  eternal, 
or,  what  is  more  probable,  as  will  afterwards  be  seen, 
co-existed  from  creation — not,  however,  as  molecular 
motion,  but  as  motion  of  the  mass. 

The  theories  do  not  account  for  the  amount  of  heat 
required. —  It  has  been  shown  that,  although  the 
materials  of  our  solar  system  had  fallen  together  from 
an  infinite  distance,  it  could  not  have  generated  heat 
sufficient  to  have  formed  a  gaseous  nebula  extending 
to  the  distance  of  the  planet  Neptune.  Gravitation 
alone  could  not,  therefore,  have  been  the  source  from 
which  the  nebula  obtained  its  heat.  The  solar  nebula, 
however,  must  originally  have  extended  far  beyond 
the  orbit  of  Neptune. 

But  supposing  it  could  be  demonstrated  that  the 
heat  thus  generated  was  sufficient  to  have  formed  a 
nebula  extending  to  even  twice  the  distance  of  Nep- 
tune, this  would  not  remove  the  fatal  objection  to  the 
gravitation  theory  of  the  origin  of  the  solar  nebula. 
For  the  facts,  both  of  geology  and  of  biology,  equally 
show  that  the  sun  has  been  radiating  his  heat  at 
the  present  rate  for  more  than  twice  the  length  of 
time  that  it  could  possibly  have  done  had  gravitation 
been  the  source  from  which  the  energy  was  derived. 


r  T\ 

UNIVERSITY  1 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  107 

This  objection  is  alike  fatal  to  the  meteoric  theory  ag 
it  is  to  all  other  theories  which  attribute  the  origin 
and  source  of  the  heat  to  gravitation. 

Evolution  of  matter. — Our  inquiries  into  stellar 
evolution  do  not,  however,  begin  with  the  considera- 
tion of  a  gaseous  nebula,  or  with  swarms  of  meteorites. 
There  was  a  pre-nebular  evolution.  The  researches 
of  Prout,  Newlands,  Mendelejeff,  Meyer,  Dumas, 
Clarke,  Lockyer,  Crookes,  Brodie,  Hunt,  Graham, 
Deville,  Berthelot,  Stoney,  Keynolds,  Carnelley,  Mills, 
and  others,  clearly  show,  I  think,  that  the  very  matter 
forming  this  nebulous  mass  passed  through  a  long 
anterior  process  of  evolution.  And  not  only  the 
matter,  but  the  very  elements  themselves  constituting 
the  matter,  were  evolved  out  of  some  prior  condition 
of  substance. 

I  have  already  given  at  some  length  the  views 
which  have  been  advanced  by  several  of  our  leading 
physicists  and  chemists  on  the  evolution  of  the  chemi- 
cal elements,  and  on  some  of  the  bearings  which  these 
views  have  on  stellar  evolution.  I  shall  now  briefly 
refer  to  a  point  on  which  I  venture  to  think  the 
theory  discussed  in  this  volume  seems  to  cast  some 
additional  light. 

If  the  elements  were  evolved  out  of  a  common 
source,  there  is,  in  order  to  this,  one  necessary  con- 
dition, viz.  an  excessively  high  temperature ;  for  the 
temperature  must  be  above  the  point  of  the  dissocia- 
tion of  all  the  chemical  elements.  "  In  the  primal 
stage  of  the  universe,"  says  Mr.  Crookes,  "  before 
matter,  as  we  now  find  it,  was  formed  from  the  protyle, 


108  STELLAR  EVOLUTION 

all  was  in  an  ultra- gaseous  state,  at  a  temperature 
inconceivably  hotter  than  anything  now  existing  in 
the  visible  universe  ;  so  high,  indeed,  that  the  chemical 
atoms  could  not  yet  have  been  formed,  being  still 
far  above  their  dissociation  point." 

What,  then,  produced  this  excessive  temperature 
in  this  supposed  ultra-gaseous  protyle  ?  It  could  not 
have  resulted  from  condensation  by  gravity.  In  con- 
densation the  heat  increases  as  the  condensation 
proceeds,  because  it  is  the  condensation  which  pro- 
duces the  heat.  But  here  the  reverse  must  have  been 
the  case,  for  the  ultra-gaseous  mass  was  much  hotter 
than  the  sun  which  was  afterwards  formed  out  of  it. 
It  was,  according  to  Mr.  Crookes,  when  this  gaseous 
mass  cooled  down,  so  as  to  permit  of  its  becoming  con- 
verted into  solid  matter,  that  condensation  into  a  sun 
could  take  place.  Besides,  was  it  not  the  excessive  heat 
which  produced  the  assumed  ultra-gaseous  condition  ? 

There  is  another  difficulty  besetting  the  theory 
that  the  primitive  heat  was  derived  from  condensation 
by  gravitation.  Supposing  we  should  assume  it  pos- 
sible that  the  protyle  could  exist  in  this  ultra-gaseous 
state  without  possessing  temperature,  and  that  it  ob- 
tained its  heat  from  condensation  by  gravity,  then  the 
fact  of  condensation  taking  place  shows  that  the  gas 
was  not  in  a  state  of  equilibrium.  But  the  gas  could 
not  have  remained  stationary  for  a  single  moment 
without  beginning  to  condense  while  in  a  condition  of 
unstable  equilibrium.  We  must  therefore  conclude 
that  the  gas  must  have  been  in  some  other  condition 
than  the  gaseous  state  prior  to  condensation. 


PRE-NEBULAR  CONDITION  OF  THE  UNIVERSE  109 

The  impact  theory  seems  to  remove  all  these  diffi- 
culties. It  is  just  as  likely  a  priori,  if  not  more  so, 
that  the  primitive  form  of  the  protyle  should  have  been 
that  of  large  cold  masses  moving  through  space  in  all 
directions,  with  excessive  velocities,  as  that  it  should 
have  been  that  of  a  gaseous  mass  in  a  state  of  unstable 
equilibrium.  If  we  assume  the  former  condition,  then 
the  colliding  of  these  masses  would  account  not  only 
for  the  ultra-gaseous  state,  but  also  for  its  incon- 
ceivably high  temperature.  Besides,  in  this  case  we 
are  not  called  upon  to  account  for  any  other  antecedent 
state  of  the  masses  before  collision,  for  they  may  have 
existed  from  the  beginning  of  creation  in  the  form  of 
masses  in  motion  through  space. 

Had  space  and  time  permitted,  it  might  have  been 
shown  that  there  are  other  obscure  points  on  which 
the  theory  seems  to  shed  additional  light.  I  shall 
now,  in  conclusion,  refer  to  a  point  wherein  the 
theory  differs  radically  from  that  of  all  other  theories 
of  stellar  evolution.  But  before  doing  so  I  may 
briefly  refer  to  an  objection  which  has  been  frequently 
urged  against  the  theory. 

Objection  considered. — The  objection  to  which  I 
refer  is  this,  that,  had  the  nebulae  been  produced  by 
impact  in  the  way  implied  in  the  theory,  then  we 
ought  to  have  had  some  historical  record  of  such  an 
event.  I  can  perceive  no  force  in  such  an  objection. 
Our  historical  records,  I  presume,  do  not  extend  much 
farther  back  than  about  8,000  years,  and  we  have 
no  evidence  to  conclude  that  a  new  nebula  makes  its 

appearance  in  the  visible  firmament  with  such  fre- 
11 


110  STELLAR  EVOLUTION 

quency;  and  supposing  it  did,  we  have  no  grounds 
for  assuming  that  its  production  hy  impact  in  the 
way  supposed  by  the  theory  would  attract  general 
notice.  It  is  doubtful  if  the  nebula  produced 
would,  in  the  first  instance,  be  actually  visible.  I 
have  shown  that  the  temperature  of  the  nebula  could 
not  have  been  less  than  about  300,000,000°  C.,  and 
it  is  very  doubtful  if  the  gaseous  mass  enveloping  all 
that  was  solid  in  the  nebula  would,  at  such  a  tem- 
perature, be  self-luminous.  The  probability  is  that 
all  the  chemical  elements  composing  it  would  be  in 
a  state  of  utter  dissociation,  and  converted  back  into 
the  original  protyle  from  which  they  were  derived, 
again  to  be  slowly  reconverted  into  their  former 
atomic  condition  as  the  temperature  fell. 

Can  we  on  scientific  grounds  trace  back  the  evolu- 
tion of  the  universe  to  an  absolute  first  condition  ? — As 
has  been  repeatedly  stated,  all  inquiries  into  the 
evolutionary  history  of  the  stellar  universe  begin  in 
the  middle  of  a  process.  Evolution  is  a  process. 
The  changes  that  now  occur  arose  out  of  preceding 
changes,  and  these  preceding  changes  out  of  changes 
still  prior,  and  so  on  indefinitely  back  into  the  un- 
known past.  This  chain  of  causation — this  succession 
of  change — of  consequent  and  antecedent — could  not 
in  this  manner  have  extended  back  to  infinity,  or  else 
the  present  stage  of  the  universe's  evolution  ought  to 
have  been  reached  infinite  ages  ago.  The  evolution 
of  things  must  therefore  have  had  a  beginning  in 
time.  Professor  Winchell,  in  his  final  generalisation 
to  his  work,  "  World  Life,"  has  stated  this  matter  so 


PEE-NEBULAE  CONDITION  OF  THE  UNIVERSE  111 

clearly  and  forcibly  that  I  cannot  do  better  than  here 
quote  his  words  on  the  subject. 

"We  have  not,"  says  Professor  Winchell,  "the 
slightest  scientific  grounds  for  assuming  that  matter 
existed  in  a  certain  condition  from  all  eternity,  and 
only  began  undergoing  its  changes  a  few  millions  or 
billions  of  years  ago.  The  essential  activity  of  the 
powers  ascribed  to  it  forbids  the  thought.  For  all 
that  we  know — and,  indeed,  as  the  conclusion  from  all 
that  we  know — primal  matter  began  its  progressive 
changes  on  the  morning  of  its  existence.  As,  therefore, 
the  series  of  changes  is  demonstrably  finite,  the  life- 
time of  matter  itself  is  necessarily  finite.  There  is  no 
real  refuge  from  this  conclusion  ;  for,  if  we  suppose 
the  beginning  of  the  present  cycle  to  have  been  only  a 
restitution  of  an  older  order  effected  by  the  operations 
of  natural  causes,  and  suppose — what  science  is  unable 
to  comprehend — that  older  order  to  be  a  similar  re- 
inauguration,  and  so  on  indefinitely  through  the  past, 
we  only  postpone  the  predication  of  an  absolute  begin- 
ning, since,  by  all  the  admissions  of  modern  scientific 
philosophy,  it  is  a  necessity  of  nature  to  run  down." 

These  are  consequences  which  necessarily  follow 
from  every  theory  of  stellar  evolution  which  has 
hitherto  been  advanced.  The  impact  theory,  how- 
ever, completely  removes  the  difficulty,  for  according 
to  it  the  evolutionary  process  can,  on  purely  scientific 
grounds,  be  traced  back  to  an  absolute  beginning  in 
time.  If  huge  solid  masses  moving  through  space  were 
the  original  condition  of  the  universe,  then,  in  so  far 
as  either  philosophy  or  science  can  demonstrate  to  the 


112  STELLAR  EVOLUTION 

contrary,  it  might  have  been  in  this  condition  from  all 
eternity.  We  are  therefore  not  called  upon  to  account 
for  this  primitive  condition  of  things.  Now  it  is  evi- 
dent, unless  a  collision  should  take  place,  the  universe 
would  remain  in  this  condition  for  ever :  without  a 
collision  there  could  be  no  change,  no  work  performed, 
and  absolutely  no  loss  or  gain  of  energy,  and  therefore 
no  process  of  evolution.  The  first  collision  would  be 
the  absolute  commencement  of  evolution — the  begin- 
ning of  the  process  of  the  development  of  the  universe. 
Evolution  would,  in  this  case,  have  its  absolute  begin- 
ning in  time,  and  consequently  was  not  eternal.  If,  on 
the  other  hand,  we  assume,  what  is  far  more  in  har- 
mony with  physics,  metaphysics,  and  common  sense, 
that  the  universe  was  created  in  time,  we  are  still  led 
to  the  same  result  as  to  an  absolute  commencement  of 
evolution.  In  both  cases  we  reach  a  point  beyond 
which  there  can  be  no  legitimate  inquiry ;  no  further 
question  which  the  scientists  can  reasonably  ask. 

We  have  no  grounds  to  conclude  that  there  is 
anything  eternal,  except  God,  Time,  and  Space.  But  if 
time  and  space  be  subjective,  as  Kant  supposes,  and 
not  modes  pertaining  to  the  existence  of  things  in 
themselves,  then  God  alone  was  uncreated,  and  of  Him 
and  to  Him  are  all  things.^  ^ 


INDEX. 


A  QUI  Range,  Utah,  fault  in,  57 
•£*-    Arcturus,  motion  of,  16 
Atmosphere,  universal,  82 

„  Dr.  Hunt  on,  86 

Mr.  Mattieu  Wil- 
liams on,  86 
Atomic  weights,   logarithmic  law 

of,  100 

Atoms,  according  to  Herschel  and 
Clerk-Maxwell,  manufactured 
articles,  92 

BINARY  systems,  32 
„  Dr.  Johnstone 

Stoneyon,33 
„  Sir  W.  Thom- 

son on,  33 
Biology,  testimony  of,  as  to  age  of 

sun's  heat,  65 
Brodie,  Sir  B.,  on  the  pre-nebular 

condition  of  matter,  84 
Brown  and  Dickson  on  sediment  of 
the  Mississippi,  40 

pARNELLEY,     Dr.,    argument 
\J    from  compound  radicles,  94 
fji  Cassiopeiae,  motion  of,  16 
a  Centauri,  distance  of,  16 
Chemical  elements,  evolution  of,  80 
Clarke,  Prof.  F.  W.,   on  atomic 
weights,  93 
w  on  evolution 

of  the  che- 
mical ele- 
ments,80, 
89 

„  on  the  pre- 

nebular 
condition 
of  matter, 
98 


Comets,  according  to  Laplace, 
strangers  to  our  system, 
17 

„  according  to  Prof.  A.  Win- 
chell,  strangers  to  our 
system,  17 

„       M.  Faye  on  origin  of,  17 
„      probable  origin  of,  17 
Compound     radicals,      argument 

from,  95 

Condensation  in  relation  to  nebu- 
la, 27 
„          the  last  condition  of 

a  nebula,  30 
Cosmical    dust    and  "  fire-mist," 

81,  102 

Crookes,  Mr.  W.,on  the  pre-nebular 
condition  of 
matter,  90-98 
„  onprotyle,  96 

61  Cygni,  motion  of,  16 

TVARWIN,  Mr.  Charles,  on  geo- 
-L'     logical  time,  67 
Denudation,  age  of  the  globe  as 
represented  by,  63,  64 

„      average  rate  of  whole 

globe,  44 
„      evidence    from    faults 

as  to  rate  of,  53 
„      Dr.  A.  Geikie   on  rate 

of,  41 

„      glacial  epochs  in  rela- 
tion to,  46,  47 
„      in  Colorado,  58 
„      in  past  ages  not  much 
greater  than  at  pre- 
sent, 44 

„      method  employed  to  es- 
timate its  rate,  39,47 


114 


STELLAR  EVOLUTION 


Denudation,  Mr.  A.  R.  Wallace's 
method  of  estimat- 
ing its  rate,  51 

„  of  Bristol  coal-fields, 
59 

„  of  Mississippi  basin, 
Sir  Charles  Lyell 
on,  44 

„         of  Pendle  Range,  60 

„          of  Pentlands,  59 

„          of  river  basins,  41 

„  of  South  of  Scotland, 
55 

„         of  Wales,  59 

„  Prof.  Haughton's  me- 
thod of  estimating 
its  rate,  50 

„  Rotation  of  the  earth 
in  relation  to,  46 

„  the  direct  method  of 
estimating  its  rate, 
52 

„          time  required  to  effect 

the  amount  of,  63 
Dewar  and  Liveing  on  dissociation 

of  chemical  elements,  83 
Dissociation  of  chemical  elements, 
Dr.  T.  Sterry  Hunt 
on,  82,  85 

„  of  chemical  elements, 
M.  Berthelot  on,  83 

„  of  chemical  elements, 
M.  Deville  on,  83 

„  of  chemical  elements, 
Mr.  Lockyer  on,  82 

„  of  chemical  elements, 
Profs.  Liveing  and 
Dewar  on,  83 

„  of  chemical  elements, 
Prof.  Schuster  on, 
83 

„  of  chemical  elements, 
Sir  B.  Brodie  on, 
82,  84 

„  Dumas,  M.,  on  essen- 
tial unity  of  mat- 
ter, 83 


EARTH'S  crust,  argument  from, 
93 
„         rotation,  its  influence 

on  denudation,  46 
Emmons,  Mr.  S.  F.,  on  a  fault  in 

Aqui  Range,  58 
Energy    existing     as    motion    of 

stellar  masses,  3 
„      transformed  by  collision,  3 
Evolution,  can  it  be  traced  back  to 
a  first  condition  ?  110 
„        evidence   of,  'from   the 
grouping  of  the  stars, 
81 

,,  from  smaller  to  larger 
aggregates  of  matter, 
81 

„        of  matter,  107 
„        of    the    chemical    ele- 
ments, 80,  107 

Tj^AULTS,  evidence  of  rate  of  de- 
nudation from,  53 
„        examples  of,  54-60 
„        "  Grand  Wash,"  Colo- 
rado, 58 

.,        in  East  Tennessee,  58 
„        in  Strathmore,  55 
Faye,  M.,  on  origin  of  comets,  17 

GASEOUS  condition  essential  to 
the   nebular  hypo- 
thesis, 25 
„          state,  second  condition 

of  a  nebula,  24 
Geikie,  Dr.  A.,  on    area  of    the 

globe,  48 

„  on   denudation    of 

the  Pentlands,  59 

„  on     examples     of 

enormous  faults, 

55 

„  on  rate  of  denuda- 

tion, 41 

Geological  epochs  of  past  ages, 
misconceptions  re- 
garding, 49 


INDEX 


115 


Geological  time,  Mr.  A.  B.  Wallace 

on,  65 

„        time,  Mr.  Charles  Dar- 
win on,  66 
„        time,     Prof.     Haeckel 

on,  67 
„         time,  Prof.  Huxley  on, 

65,  66 
„        time,    Sir    Andrew    C. 

Kamsay  on,  67 
Geology,  testimony  of,  in  regard  to 

age  of  sun's  heat,  39 
Glacial  epoch,  age  of  the  earth  as 

determined  by,  64 
„      epochs,  influence  on  denu- 
dation, 46 

Gravitation  does  not  account  for  the 

heat  required,  106 

„         does  not  account  for 

motion  of  the  stars, 

105 

„  insufficient  to  account 
for  heat  of  nebulas, 
27 

Groombridge  1830,  motion  of,  15 
„  not  an  eject,  106 

„  Prof.      Newcomb 

on      motion 
of,  15 

Grove,   Sir  W.    B.,   on  the  pre- 
nebular  condition  of  matter,  78 

HAECKEL,  Prof,  on  geological 
time,  67 

Haughton,  Prof.,  method  of  esti- 
mating rate  of  denudation,  50 
Heat,  age  of  the  sun's,  37 
Helmholtz  on  age  of  sun's  heat,  35 
Huggins,  Mr.,  and  Dr.  Miller  on 
spectra  of  nebulae  with  one  ni- 
trogen line,  84 

Hull,  Prof.,  on  denudation  of  Pen- 
die  Bange,  60 
on  examples  of  enor- 
mous faults,  54 

Humphreys  and  Abbot  on  sediment 
of  the  Mississippi,  40 


Hunt,  Dr.  T.,  on  the  pre-nebular 
condition  of  mat- 
ter, 85 
„        on     universal     at- 

mosphere,  86 
Huxley,  Prof.,  on  geological  time, 

65,66 
Hypothesis,  value  of,  70 

"TMPACT     Theory,"     why     so 
called,  2 

„  in  relation  to 

theories  of 
pre-nebular 
condition 
of  matter, 
102 

,,  removes  diffi- 

culties re- 
gar  ding 
origin  of 
heat,  108, 
109 
e  Indi,  motion  of,  16 

T7ING,  Mr.  Clarence,  on  the  Wah- 
-"-    satch  Fault,  59 

T  ALANDE  21185,  motion  of,  16 
-Lj        „         21258,     motion     of, 

16 
Laplace,  M.,  on  the  heat  of  the 

solar  nebula,  30 
Lavoisier,  M.,  on  simpler  forms  of 

matter,  86 

Lesley,  Mr.  3.  P.,  on  a  fault  in  the 

Appalachians,  57 

„  on  fault   in  East 

Tennessee,  58 
Liveing  and  Dewar  on  dissociation 

of  chemical  elements,  83 
Lockyer,  Mr.,  on  arrangement  of  the 
planets  according 
to  density,  25 

„  nebulae  with  solid 
matter  in  a  gase- 
ous mass,  20 


116 


STELLAR  EVOLUTION 


Lockyer,  Mr.,  on  essential  condi- 
tion of  solar  ne- 
bulae, 25 

„  on  hypothesis,  70 

„  on  number  of  me- 

teorites, 103 
„  on  outburst  of  stars, 

33 

,,  on  "  sorting  "  of  the 

chemical    ele- 
ments, 25 
Lodge,  Prof.  0.,  on  ethereal  origin 

of  matter,  87 

„  on  the  pre-nebular 

condition    of 
matter,  87 

„  on  vortex  atoms,  88 

Logarithmic  law  of  atomic  weights, 

100 

Lyell,  Sir  Charles,  on  denudation 
of  the  Mississippi  basin,  44 

MACVICAB,    Dr.,    on    ethereal 
origin  of  matter,  87 
Matter  not  probably  eternal,  112 
Mendelejeff,ProfM  on  Periodic  Law, 

96 

Meteorites,  number  greatly  exag- 
gerated, 103 

„          probable  origin  of,  12 
„          Sir  H.  Eoscoe  on  con- 
stitution of,  12 
Sir  W.  Thomson  on,  12 
Mill,  Mr.  J.  S.,  on  hypothesis,  70 
Miller,  Dr.,  and  Mr.  Huggins  on 
spectra  of  nebulae  with  one  nitro- 
gen line,  84 

Mills,  Dr.,  on  Polymerisation,  95 
Morris,  Mr.  Charles,  on  the  pre- 
nebular  condition  of  matter,  75 

NEBULAE,  broken  fragments  in 
a  gaseous  mass,  19 
„  cometic,  22 

„  condensation  insuf- 

ficient to  account 
for  heat  of,  27 


Nebulae    condensation,    last    con- 
dition of,  30 

„         first  condition  of,  19 
„         gaseous  state,  second  con- 
dition of,  24 
globular,  21 

„         heat  of,  not  due  to  gravi- 
tation, 27 
,,         how  they  occupy  so  much 

space,  18 

„         how  origin  of  by  impact 
might  not   have   been 
observed,  110 
,,         must  possess  an  excessive 

temperature,  26 
„         Mr.  Lockyer  on,  20-22 
,,          origin  of,  18 
„         Prof.  A.  Winchell  on  me- 
teoric origin  of,  22 
„          Prof.  Tait  on,  20 
,,         Sir  W.  Thomson  on  origin 

of  6,  28 

„         spheroidal,  22 
„         why     of     such     various 

shapes,  19 

Nebular  hypothesis,  gaseous  con- 
dition essential  to,  2,  5 
Newcomb,    Prof.,    on    motion    of 

1830  Groombridge,  15 
Newlands  on  Periodic  Law,  96 
Nova  Cygni,  on  sudden  outburst  of, 
33 


0 


EJECTION  considered,  109 


"pAL^EOZOIC  times,  winds  pro- 
•t      bably  not  higher  than  at  pre- 
sent, 46 

Peach,  Mr.  B.  N.,  on  examples  of 
enormous  faults, 
55 

„  on  denudation  of 

the      south     of 
Scotland,  55 

Periodic  Law,  argument  from,  96 
„        Prof.  Mendele jeff  on  96 


INDEX 


117 


Periodic  Law,  Newlands  on,  96 

„  Prof.  Keynolds  o»,  96 

Planets,  on  their  arrangement  ac- 
cording to  density,  25 
Polymerisation,  argument  from,  95 

Dr.  Mills  on,  95 
Pouillet,  on  rate  of  solar  radiation, 

35,2 
Powell,  Major  J.  W.,  on  denudation 

of  Uinta  Mountains,  58 
Pre-nebular  condition    of    matter, 
Dr.    G.    Johnstone 
Stoney  on,  99 

„         condition  of  matter,  Dr. 

T.  Sterry  Hunt  on,  85 

„         condition  of  matter,  Mr. 

Charles  Morrison,  75 

„         condition  of  matter,  Mr. 

W.  Crookes  on,  90 
„         condition    of    matter, 
Prof.  A.  Wmchell  on, 
71 

„         condition    of    matter, 
Prof.  F.W.Clarke  on, 
98 
„         condition    of    matter, 

Prof.  Lodge  on,  87 
„         condition  of  matter,  Sir 

B.  Brodie  on,  84 
„         condition  of  matter,  Sir 
W.  E.  Grove  on,  78 
„         evolution,  107 
Proctor,  E.  A.,  on  meteoric  origin 

of  solar  system,  23 
Protyle,  the  primal  matter,  96 
Prout's  Law,  argument  from,  92 


•DAMSAY, 


Sir      Andrew      C., 
on    denudation 
of  Bristol  coal- 
fields, 59 
„        on   denudation  of 

Wales,  59 
„        on      geologica 

time,  67 

Eeynolds,  Prof.,  on  Periodic  Law 
96 


Eogers,  Prof.  H.  D.,  on  a  great  fault 
in  the  Appalachian  coal-fields, 
57 

Eoscoe,  Sir  H.,  on  constitution  of 
meteorites,  12 

Eotation,  supposed  influence  on  de- 
nudation, 46 

SAIGEY,  M.,  on  ethereal  origin 
of  matter,  87 

Schmidt,  Dr.,  on  number  of  me- 
teorites, 103 
Solar  nebula,  M.  Laplace  on  heat 

of,  30 

„  Mr.  Lockyer  on  con- 

dition essential  to, 
25 
„  Sir  W.  Thomson  on, 

6,28 
Solar  radiation,  rate  of,  according 

to  Pouillet  and  Langley,  35 
Solar  system,  Mr.  E.  A.  Proctor  on 

meteoric  origin  of,  23 
Star  clusters,  34 
Stars,  evidence  of  evolution  from 

their  grouping,  81 
„      how    origin   of    by  impact 
might  not  have  been  ob- 
served, 110 

,,      in  four  groups,  81 
„      motion  not  accounted  for  by 

gravitation,  105 
„     motion    not    due    to    their 

mutual  attractions,  14 
„      motion  of,  how  in  straight 

lines,  14 

,,      sudden  outbursts  of,  33 
Stoney,  Dr.  G.  Johnstone,  on  the 
pre-nebular  condition  of  matter 
99 
Subaerial  denudation,  method   of 

estimating  rate  of,  39,  47 
Sun,  age  of  heat  of,  34 
Sun's  heat,  age  of,   according  to 

Geology,  37 

„        age  of,  a  crucial  test,  34, 
37 


118 


STELLAR  EVOLUTION 


Sun's  heat,  age  of,  according    to 

Thomson    and  Tait, 

35 
„        age  of,  as  determined  by 

Biology,  64 
„        age  of,  as  determined  by 

Geology,  39 

rPAIT,  Prof.,  nebula?    with    solid 
matter  in  a  gaseous 
mass,  20 
,,  on  age  of  sun's  heat, 

35 
Temperature  excessive,  essential  to 

nebulae,  26 
„  produced  by  collision, 

5 
Thomson,  Sir  W.,  on  age  of  sun's 

heat,  35 

„  on  meteorites,  12 

„  on  origin  of  so- 

lar nebula,  28 
„  on  solar  nebula, 

6 

„  suggestion  by,  86 

Tides,  supposed  influence  on  de- 
nudation, 45 
Tycho  Brahe,  on  sudden  outburst 

of  a  star,  33 

Tylor,  Alfred,  on  the  denudation 
of  Mississippi  Basin,  40 


u 


INTA  Mountains, 


denudation 

of,  58 
fault  in,  57 


VOKTEX  atoms,  Prof.  Lodge  on» 
83 


"TTTAHSATCH    Fault,"    Utah, 

•  ^      immense  dislocation,  58 
Wallace,  Mr.  A.  B.,  on  geological 
time,  65,  68 
„  method  of  es- 

timati  ng 
rate  of  denu- 
dation, 57 
Williams,  Mr.  Mattieu,  on  universal 

atmosphere,  86 
Winchell,  Prof.  A.,  on  age   of  the 

.   earth,  64 

„  on     comets 

strangers     to 
our  system, 17 
„  on   denudation 

of  Colorado 
plateau,  58 

7t  on     deposition 

of  Palaeozoic 
sediment,  45 

„  on  ethereal  me- 

dium, 87 

„  on  meteoric  ori- 

gin of  nebula?, 
22 

„  on  nebular  hy- 

pothesis, 69 

„  on     the     pre- 

nebular  con- 
dition of  mat- 
ter, 71 


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